well keeping it as simple as possible, no buffers, you'd just run a synchronous or a multiplier of, the 7Mhz clock, so 14/28/56Mhz etc.
but as you're not replacing the 68000 given that it's soldered onto the board, it's still "live" - you're adding something else onto it's bus. You'd have to have some basic logic to negotiate control of the bus with/from the original 68000 and put it to sleep. same for the 1200 with it's onboard 020.
i don't know how much more it would need from there to buffer the original 7Mhz side of the control logic and allow whatever you like on the other side:- be it an actual 25Mhz bus with 030 and some zero wait state fast ram or whatever.
