I forget; was it the 80387 or the 80487 that was just a full-blown DX (as in, FPU included on the die) version of its 80_86SX counterpart with only subtle differences in the pinout so it could disable the onboard main/SX processor socket?

Edit: Found it! It was the i487 SX:
https://www.youtube.com/watch?v=cwkZz4uwcuQ