I got luckey with mine I guess. I was undercoated and I have not found a rusted out area. It seems it is a rare bird. It had been hit in the front and the body work was not the best but it is functional.

Rust in those areas is not uncommon. Check out the resoration forum at http://www.celicasupra.com/phpBB2/
and ask the guys there that question. There are some who drag race, autoX, and even a few drifters on the board who may have some first hand experiance racing after repairs.

With the mods we are allowed you really don't load up that much more that you would in a little spirited driving on a winding mountain road. You should be ok as long as the repairs are made properly.

The sunroof route I took may not be the best but it worked for me. I removed all the tracks, frame, motors, and hardware. Then welded the outer panel in place and filled the gaps with 3M body filler. A little elbow grease, some sand paper, and few cans of paint and it looks like a hardtop under casual examination.