Well since no one replied to ths thread for possible solutions, I will show you what we did for future reference.
In the end, we adapted the stock Fiero sliders to the recaros.
The recaro seat has 6 mounting point on it. Two hole about an inch apart in the front and a hole in the rear on each side. In comparison to the stock Fiero seats, these holes are about 7cm wider total.
So what we did was take some pieces of 2" wide 1/4" thick stock, cut 8 pieces of it about 2.5" long (I can't remember any of our exact measurements). We then used a drill press to drill holes to mount them to the Recaros.
From there, it was a matter of lining up stock brackets, tack-welding them on, and test fitting. We found that we had to offset the brackets towards the inside since the seats were a bit wider than the stockers. We also had to cut down part of the upper plate that we used in order for the levers that the sliders use to have full movement.
The final modification we had to do to the brackets was to notch the mounting holes on the floorplates, because once again, the seats were wider and have more leg bolster.
I would like to thank my friend Matt of the Michigan Volkswagen Enthusiasts who did the welding and most of the fabbing.
Heres the obligatory pics to help explain what I typed:
Stock Seats:
This is a pic of the brackets with the four plates tack-welded on awaiting final welding. You can see the notches we had to make for the levers. You can also see the notched floorplates.
A couple more closeups of the plates both before and after final welding:
Action shots of Matt welding:
The completed brackets mounted on the Recaros and ready for installation:
Installed Seats:
I do sit a bit taller in these seats due to more padding, but there is no sacrifice in range of motion. I'm 6'3" and I still fit ok, but it's just a bit more snug now. But the seats are far more comfortable.
Hope you enjoy.
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'88 GT- 257rwhp 319rwft/lbs 12.95@106.1mph