A 68882 will work in place of a 68881. They are pin compatible. The 68882 is a more efficient update to the 68881 that is capable of scaling to higher clock speeds. The instruction set is the same as in the 68881. This is why a 68882 is preferable to a 68881 if you can find one. Your floating point results will always be better with a 68882 at the same clock speed. If you can upgrade your machine to a full 68040, though, that would be the best upgrade of all because apart from the obvious advantages the 040 has over the 020 and 030, from a purely floating point standpoint the FPU in the 68040 is far faster than even the fastest 68882 and can be accessed more quickly because it is on die.