Reading the post before commenting would be smart
The 40mhz 386 fpu was pretty rare, I originally purchased one for my state of the art 386 and it was a few hundred dollars at the time and sped up EXCEL spreadsheets quite a bit. I was lucky enough to find a 386/40 amd motherboard with FPU last year for my retro PC game box. I think the FALCON series of games were the only ones that even used the FPU for anything just like it was the first to use dual cpu's.
Of course I dont think it would fit in a 68030/50 board unless you use a hammer and dont mind smoke when powerd up. The fastest 68030 used on the mac was 40mhz (on the IIfx) so finding a 50mhz fpu there wont happen.