Sounds like a great project, many people have speculated about doing this and its effects/requirements (patched ROM to translate 040-specific instructions?) but no one actually got round to doing it! It would be great if you posted your results somewhere!!
I guess a good starting point would be to do a ROM dump from Basilisk running in 68060 mode as it will have patches to 68040-specific instructions like FPU state frame layout or PTEST. Then write it to a custom, programmable ROM SIMM using
Not too sure about the clock multiplier though, as Classic Mac OS uses the 68040 in supervisor mode (and would undoubtedly do the same with a 060), and clock multiplier is only available in user mode (68040 compatibility mode) from what I read. So it could be that the 50Mhz clock has to be supplied directly by a PLL or crystal to the 060 rather than using the bus clock which would be doubled in 040 mode.
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