The least expensive wat to lighten up factory brakes is the former AR Engineering, now Dr. Diff wilwood dynalite caliper adapter.
I just swapped out an aluminum radiator for the OEM unit and that is significant. I can lift the AL radiator with the shroud and fans into the car with one hand.
Hole sawing the bumper brackets takes out a big of weight and is not costly if you have the tools.
I always wondered if taking the inner fender wells out of any car of this era did to the underbody aerodynamics. I do agree that the frame needs to be tied to the main cage structure however those bars can be run outside of the wheel well so they don't clutter up the engine bay. It's easy to build some outriggers in the wheel well if you have some 2x3 box tubing. Also, there is a place called (Doug) Winslow racing that lays up inner fender splash shields in carbon fiber. They are $300 or so last time I checked however the craftsmanship is very nice.
Otherwise for low buck weight removal you are drilling holes and looking for brackets that can be inexpensively and safely replicated in aluminum.