It looks like you might have finally met your match. Wonder how much positive caster you now have? Would be a lot as you have it mocked up in the photo.
Interestingly, it looks like if you were doing rear steer and had the spindles swapped left to right it would appear to work. Makes me wonder (in my case) about adding coil overs and loosing the factory upper control arm/spindle/coil. Then notch the shock towers for the added header clearance, which is my car's current weakness. Reuse the factory steering parts. Would love to find an easy way to throw some big high ports on mine.
I'm not sure on the caster thing...but I'm betting it's pretty close to factory to be honest. The strut is mostly sitting right where it's pointed by the spindle...and the steering arm is pretty much level as it should be. I need to take a look at a factory SN95 if I can find one, to see how much travel that arm has vertically through its range of motion on the car it was designed for. Caster is really the one setting I don't have a ton of adjustment for...at least not to reduce it. I've got about 3/4" of positive adjustment left.
On swapping the spindles...there's two problems with that. First...it would screw the ackerman up...badly. Second, the strut brackets are angled side to side. If you swapped them, it would point the strut forward, instead of backward. I don't think this solution is possible.
Now...worst case, I do have another solution. It involves shortening the lower control arms to intersect the frame, and adding a rear facing strut bar that will also mount on the frame. This would basically turn the LCA into a rear biased triangular unit (its actually a forward biased triangle from the factory with the strut rod). Here's a picture on my friend's 67 Cougar to illustrate what I mean:
His LCA mounts are installed on the frame above the bottom of the rail. Mine would be below, and as near to the inside of the frame rail as I could mount them, to maintain the right suspension geometry with my spindles (his are Strange light duty spindles...its a track only car). This would also allow the Mustang II rack to be used pretty much unaltered as far as the pivot points go. Still...this is a last ditch fix, since I'd prefer to keep this as bolt on as possible.
I'm going to go outside later today and rough mount the rack (going to take some creativity there!) to see how badly they intersect at various LCA/rack positions, with various amounts of turn etc. Ill let you know how it goes...just keep your fingers crossed for me that there's a sweet spot, lol!