I bought a set of Pro Topline 180's to put on my 66 mustang a few weeks ago. The heads were fresh and I got a good price on them, so all was well. I pulled my old heads over the weekend to get things ready for the PTL's. I went ahead and test fit the headers to the new heads (off the car) just to check things. Passenger side looks good, Drivers side....damn header won't even bolt up to the head without hitting the plugs. I'm using autolite 3923's and hooker comps for a early mustang. So, I'm gonna try some of those short accel plugs, maybe double or triple stack the header gaskets, buy a new set of plug wires with 90* boots, and see where that gets me. Probably still have to massage the #6, 7, and 8 tubes. I took the header off, grabbed a head gasket, and proceeded to check piston-valve clearance. No dice there either. I went ahead and put a call in to Isky cams to rent their notching tool, I have to notch intake and exhaust eyebrows, the existing eyebrows are too small. Running a 1011-2 gasket, .512 lift on the cam, piston sticks .017 out of the hole. Its no fault of the heads, I guess this is just the sort of thing you run into sometime with performance parts. Sure is frustrating and expensive. I hope my exhaust pipes and all don't hit the crossmember, the PTL's have a 3/8" rasied exhasut port. With the kind of luck I've been having, I'll probably have to rework that too.