The greatest issue that I believe exists in making the 68060 compatible with the NeXT is the fact that the NeXT uses a multiplexed bus (which just gets my ire up. Saved a few bucks in the manufacture of a $10k computer and decreased the bus speed). The NeXT has CDIS low upon reset which sets the multiplexed bus mode. More importantly, there are different setup between the devices. 68060 manual 11.2.2 is a bit scary in this regard.

And the quote from 11.2.5:
The MC68060 does not implement the DLE functionality of the MC68040. Applications that use the DLE mode are not upgradable without using external logic.The MC68060 does not implement the muxed bus functionality of the MC68040. Applications that use muxed bus mode are not upgradable without using external logic.

The 68040 muxed mode is shown in the 68040 manual in Figure 7-46. /TS is low and /TA is high when the address is valid on the rising clock edge. Using the 68060, I am pretty sure that I can use BCLK to get the logic that I need to multiplex the bus. The 68060 manual has section 7.11.1 that is the 68040 arbitration protocol. I need to read through 7.11.1 and then figure out how to get the whole thing to come together.

Basically, I need to make figure 7-15 in the 68060 manual look like figure 7-46 in the 68040 manual.