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Discussion Starter #1 (Edited by Moderator)
While I had my 67 Mustang stripped to bare metal, doing the body work, I decided to add the Shelby GT/Californial Special quarter caps and deck lid to my car. I always thought the California Specials were cool, always wanted one. I had an old school snorkel hood scoop on the car and in the 80s it probably was cool (I had one one my 68 Fast Back back in the day), but I wanted something less obtrusive that would still cover and let the 532 Big Block breath.
I went with the 3 inch cowl, and I think the CS decklid will flow perfectly with the cowl hood I bought from Mustangs Unlimited.

I did some research, looked at all the supply houses, and found this stuff is pricey. Online, there are a lot of opinions about the quality of the parts etc as well. I found Fiberglass Specialties on line, and gave Mark Fastow a call. I found that Mark actually makes a lot of the parts for CJ Pony, MU and others. The hood I have is one of his, and it is a quality piece of glass.
So I ordered the side scoops, decklid and quarter caps, cheaper than the Mustang houses. Mark is very up front, like any part, there is work to be done to make it fit and look good, so no surprises. He did tell me that he left too much material on the parts so it's a matter of cutting/sanding down vice building up to make it fit.

The stuff showed up, and it looked really good. The finish was nice on all sides, not a lot of mold release, excess glass and fillers etc.
So I got started, my research and Ford Muscle friends had told me the side scoops were job. You have to remove the windows and regulators to get the fake side scoop vents off. That was fun, but needed to be done anyway.

Next step was locating the scoop on the side of the car. The side scoops are attached by one threaded rod that requires the drilling of a hole through the body between the fake scoop holes. Locating the position of the scoop is a interesting decision. First, I pushed a piece of cardboard over the stud and flush with the mating edge of the scoop. Then I traced the edge of the scoop onto the cardboard, removed the board and cut out my template to include locating hole. Then its just a matter of moving the template around to the location "looks like the ones in the pictures". Maybe some dimensions somewhere but I couldn't find em.

Now the you can mount the scoop, you will see it doesn't fit flush, I then marked the contact points with sharpie, and started sanding a lot, placing on the car repeating etc. I kept doing this until I got it to fit the contours of the body. Once I got the excess removed, I had a better idea of fitment, so I actually re drilled another hole and relocated the scoop a little more forward. Then did some more sanding.

Once I had it really close, I then taped off the car with blue tape where the scoop mated to the surface. I mixed up some of my U Pol flyweight Gold filler, and back filled the scoop. Meaning I libererally spread filler along the edge of the scoop, much like scraping peanut butter off a knife! I then mounted the scoop, snugged the nut down pretty tight and squeezed the filler out of the gaps. Let it dry good. Then you just pop it off, and the outside edge to remove the excess, and you have a perfect face.

I then painted the edge with a layer of thickened poly fiberglass resin to make it weather tight. I didn't seal the bottom gap as tight, so if water does get in there, it can get out. Repeat the process for the other side, for this, I measure the bolt hole location of the final fit, and marked it on the other side, then just to be sure I made a new template (the studs may not be exactly located on the scoop so do this) and marked it. It worked out fine.

I sweated the gaps and seams for both the scoops and side caps, Mark at FS told me that the originals were not that well put together, so I googled some photos of CS and GT cars, he was right, but I made mine as tight and symmetric as I could.
Mark will tell you the quarter caps are the biggest challenge. First you have to locate and set your decklid. You will need two gaskets for this to keep it level. Hint, I used one, just folded them over on itself on the sides to make it work. Then just set it like a stock lid, getting the gaps evened out.

Once your deck lid is straight, you will find your quarter caps are no where close to fitting. You may have to tweak the studs in the direction you need t close the gaps, but take some of the excess glass off first.

The biggest obstruction is the radius that follows the stock curved taillight panel. Again, hit the contact points with a sharpie and start sanding but go easy, it comes off quick with 80 grit and a die grinder. Once you have the radius close, start watching for contact points along the trunk face, the outside quarter panel etc, and just work the contacts down. Once you get it where it fits, and it takes a lot of work to get it to fit all the way down along the quarter to the vlance panel, you back fill with filler just like I did with the scoops.

What the backfill does is (a) provides a nice flush finish (b) creates a flat lip inside the scoops/caps the give you some strength and surface to sand against (c) allowed me to put a gasket on the face of the quarter cap that otherwise you can’t.

The driver side of my quarter gap stuck out a tad even when everything else lined up, so I was able to sand it down (1/16th of an inch?) without fear of sanding through the wall of the cap or weakening it.

Once I had the quarter caps and deck lid on, it looked great. However, it was missing something. When, I looked online, I saw a photo of the decklid and quarter cap with the little lip or ridge that runs along the edge of the lid. I figured that made the big flat spoiler back look a little less add on.

So, I got to figuring, I measured the ridge on the quarter caps, about a 1/2 wide and 1/4 inch thick. I made a template of the quarter cap ridge by transposing this onto blue tape to make a template.

Then I purchased some quarter inch balsa wood and started marking and cutting out a pattern for the quarter caps, and using a straight piece of half by quarter across the deck lid. I glued this to the car with clamps and resin, then coated it with a coat of resin, layer of glass, followed by another coat of resin. Then you start sanding. This was a lot of work again, but in my opinion well worth the effort.

I think the deck lid edge got the good idea fairy got shot on this one, until I started researching mini tubs.
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