Welcome to the site.
Building with a Fiero "tub" is another option. This involves using the drivers compartment of a Fiero and the front portion of the frame and build a custom tube frame off of the back of the tub. This allows for you to build the rear frame around what ever engine you want to use and you still retain the tub that Pontiac spent millions in development costs to design years ago. The tub is also what holds the VIN number which can help you title and register the car (a major problem is some states). The Fiero has a lot of suspension modifications that are basically bolt on so unless you want to pay someone to figure all of that out later on, you might want to consider this. If you go the Fiero route, make sure you buy a really solid Southern or West coast car that has no accident damage or rust. I can tell you first hand that after I add up the hours and dollars associated with stretching a frame and then modifying everything to accommodate rear mounted radiators, engine and transmission swaps etc, going the route of using a custom rear is the way to go and in my personal opinion will give you a better car at a lower price.
As for the body.. make sure you do your homework on all the OEM vs. donor parts that you'll need to finish it. The G28 bodies may not be 100% accurate, but this is mainly due to the number of lower cost donor parts that they use. Yes there are more accurate bodies out there but you'll be forced to buy stuff like OEM glass etc and this can be very expensive. If you can afford it... then go for it, OEM is the way to go for overall fit and finish. Keep your build diary updated and we'll all cheer you on and help along the way.
Best of luck on your build journey and again... welcome aboard.
Chris
