well, this is my personal opinion based on past experience with high horse power vehicles,
I would be wanting a custom tube chassis designed to handle the amount of torque that sort of horsepower can dish out.
a cut and modified chassis that is a few decades old... regardless of its apparent condition, would not be my first or last choice to say the least.
not to say that it hasn't been done or that it should not be done, but my recommendation for something of that caliber would be a custom chassis without question.
so, assuming you dont blow the clutch or break axles and assuming you actually hook up on the pavement... then the next thing that will happen is your frame is going to want to twist like a cork screw, if you feel that a partial fiero chassis with all its original integral roof/frame cut away then augmented with post welded frame implements will be adequate to absorb the horsepower and revert it back to the wheels without again breaking something down the line.
i am all in to see what you come up with. but i am just saying, if it were me, i would be going tube chassis...and in fact... that is what i have and i will be lucky to hit 450hp with the design of my engine, but the frame and all the mounts are fairly over designed to take that mild abuse compaired to what you are going to put your frame through.
just voicing my opinion because you asked...