[PJS50]

Semper,
If done/shimmed "right", I have seen the Finishline glass work very well on an SPF (early car; #245-ish)..
The only thing that had to be changed was the locations of the side "hooks" which the soft top buckles grab on to.. Otherwise, it looked like "factory SPF"...

1715,
Did you get you windshield situation all figured out?
When you wrote: "The windshield on my car is actually a different shape than the other windscreens, and is wider at the bottom that the new replacement one that I purchased. Shims would actually make the problem worse because of this."

It seems to me that this is exactly the type of situation where shims WOULD work... If you mount the new windshield "legs" to the inboard side of the under-dashboard brackets, then you would shim the "gap" between the bracket and the windshield leg... Right?
Were your original windshield legs bolted to the outboard side of the mounting bracket? If so, those brackets themselves are only probably 1/8" thick, so if you took the new windshield legs (which you said are @1/2" narrower than the originals; meaning they are 1/2" closer together) and mounted them to the inboard side of the mounting brackets, you really only have about 1/4" (total gap) to make up between the 2 brackets and 2windshield legs which means your shims are actually only @ 1/8" thick per side (1/2" minus @1/4" total for the thickness of the 2 mounting brackets because you are mounting the new legs to the inboard side of the bracket instead of the outboard side like before) right?

The ONLY (real) differences between the early car windshields and the later car windshields involves:
1). The height of the actual glass itself, as if measured from the top-center of the glass to the bottom-center of the glass (as measured along the surface of the glass itself).
2). The bottom, cowl following "curve" that the bottom windshield frame rail makes. The early cars had a "flatter, larger radius" curve to them. The later cars had a "taller cowl" so that Big Blocks could fit under the hood better, and thus have a "sharper, smaller radius" curve to them...
Besides this, the 2 generations windshields are essentially "identical" in terms of overall width and shape...
There is ALWAYS some shimming to do when mounting them however....