Metal removal at rear, opinions

[Ivan141]

That's where I was heading with my story... once you have a caged racecar, the world is your oyster as far as weight reduction is concerned.
In that case: yes, chop the whole lower rear end off, it will shave a few kg's off. I would advise a rear undertray or at the very least some ventilation holes in the rear bumper. With the original fuel tank out of the way, you're left with a great big void with a bumper behind it (kind of like a parachute).

That still doesnt change the fact that you're better off shaving weight off the front of the car. The rear is always easier to lighten, but you end up with a big front weight bias (great for drifting though ;-))
The headlights are pretty heavy on a trueno, so that's another thing to consider for a race car (if you haven't gutted them already).