77 Firebird Formula Project

[77Bird]

Hi All
I have bought a 77 Formula T-Top car which came with a 350 v8 and auto trans.
My plans are to build a street cruising / show car with all the modern touches and retro look with more power via either LS3 and Supercharger or LT4 and auto trans.

I will be mini-tubbing the car too, just ordered the DSE kit from Summit Racing.
I want Coilovers, and big Wilwood brakes all around

The car is in excellent condition, no rust.

The advice I need is should I order a complete chassis which I know is over built for my use, however I may do some auto cross events down the road, or should I just replace the subframe and a 4link rear end. I was thinking for using a 9” rear end

I want to build the car once and I want it structurally sound for the added power

I appreciate any advice.