I had to redo the floor panel on my '88 Tristar and inserted a 2" angle, 1/8" thick at the forward edge of the floor panel (fiberglassed and bolted to the new pt wood) and thru-bolted the floor portion of the hinges to it. I trimmed the height of the angle to match the floor panel thickness. Inside the motor box I used a piece of 1/8"x2"x20" alum. flat bar (continuous for both hinges) and thru bolted the box portion of the hinges to that. I don't have the gas shocks on mine though. Probably not a simple fix for yours.
1988 Tristar 190 Sport, 351W w/GT-40's, 1:1 Velvetdrive