Yes back in 2006 I was pretty sure you could not make weight in a rx7 and my shell was pretty beat up so I did a rotisserie build with intent of proving you could not make weight. Well I failed. I managed to make weight with a 240 pound driver, but it was a lot of work. You have to look at every part on the car and see if you can make it lighter legally.
I used a 79 shell which seem a little lighter but updated all the front sheet metal to late as the front bumper is lighter.
Are your Doors gutted? 18 pounds per door.
When I researched batteries I searched the Auto Palace sight for batteries for the car and found a 20 pound spread.
Susko had a sway bay design using a modified stock front bar that is 6 pound lighter than a 1 1/8th bar.
No rear bar.
Undercoating and sound deadening.
I use a 8 gallon cell but I can swap my 12 back in for longer races.
Are you using a panhard bar, the watts link bracket welded the frame looks pretty heavy to me.
All the parking brake brackets on the frame are gone.
Six pounds by legally trimming the wiring harness. Took 20 hours with the harness on the bench.
Aluminum Radiator.
No front strut bar, I do not believe they help
I have left some stuff on the table too. Exhaust could be lighter but I like quiet.
I still have old school gauges, I could go to a data system.
There is really no single magic bullet, and it is certainly easier if you are building a new shell, but it is looking at every part and seeing what you can do.