I all ready see you waisting money!
Fiberglass is not worth it except for the hood so you can put that money elsewhere. If it is going to be track only car for sure then you could gut the dash. If that's what you want to do so be it.
You want track only car, fast......why are you putting a 6pt cage in there? Do it right the first time and at least put a 8-10pt. with 10pt. being my choice.
Is this for a 1/8 or 1/4 mile car? What kind of trans
do you want to run? (manual or auto) What size gear depends on what trans
setup you choose. Do you want to be able to run pump gas? A custom drive shaft will have to be made no matter what trans
you select. Foxes didn't come with a BB! The rear end needs to be a beefed 8.8 min. or a mild/wild 9".
Need to get an aftermarket K member for it to fit well in there. Any will do supporting a 5.0 motor. Of course the oil pan for it too.
Make sure you have a suffiecient fuel system cause these motors are thirsty.
There is a ton more to be considered but ask yourself these questions then you can move into the actual motor build.