[colejohnson66]

The ROM used different sized transistors to store two bits per transistor. That's pure analog territory, which most HDLs don't touch.

[JdeBP]

And largely irrelevant if the goal is synthesizing something that can be put onto an FPGA to be a workalike for the 8087. It's almost never about synthesizing the exact original hardware to be fabricated. See CPU86 and Zet, for examples:

* https://github.com/nsauzede/cpu86/wiki

* https://github.com/marmolejo/zet