[Landseer]

Ditto on the tuneup. As Danglerb says.

On the gas tank --- carving on that gas tank to avoid spending money on a missing gas cap? Buy the cap. Clean the tank. Your fuel pump is $250 to replace and it will likely fail in several months because the strainer built into the discharge fitting is too coarse to prevent debris from entering the pump and, like russian roullette, jamming it.

In general ----
Part of the reason Porsche could accomplish the performance on these cars is singular engineering of every part, with few exceptions, and morphing of the parts year to year as needed to accomplish other enhancements.

Starting to carve on them is a slippery slope. You can rig stuff and it might work, but the degradation of the car will be irreversible.

These are not chevelles.