I had a conversation with the developer AmiBerry (Dimitris Panokostas), about this topic.
He recommended taking the code CPU from the github.com/aranym/aranym project as a basis,
as the most perfomance and functional CPU 68040.
I think that in the first step can take the code from the github.com/aranym/aranym/tree/master/src/uae_cpu directory, add FASTRAM to it and build it . And the second stage is to try to integrate it with the FPGA core.