Hmmm. I believe FPU's are normally intended to run at a higher frequency than the CPU - Eg, normal A1200 has a 68882 on a A1200/4 clocked at around 33Mhz. On most 68030@50Mhz boards the FPU's are also ran at 50Mhz.
EDIT: Im sure I saw that in a 68882 datasheet somewhere...Might be wrong though...
That empty socket will need a crystal for the FPU...Whatever frequency the FPU is...
Putting a incorrect FPU (That is, forcing it to run at a higher frequency) into a card, even if the FPU is rarely used by the system, could result in a toasted FPU and/or other components.
Mismatched clock frequencies also have a tendeny of resulting in data communication errors between IC's.
To be safe Id recommend that you try to get a 50Mhz FPU (And associated crystal) for your card...And make sure that its the correct pin configuration (PLCC or PGA).
Hodgkinson.