I thought that was interesting (with appropriate caveats) when I read about the aero-sprite too.
dtmerritt, your car might be suitable for a $20ish, 1 hour to install,
5th gear swap.
But otherwise I'm guessing the buick was a 3 speed, so you would have to look at the pinto 4 speed and the buick 3 speed from that era and figure out the nuts and bolts. If the pinto 4th gear and buick 3rd gear are direct drive, it might not have been too "lossy".