All Amigas Kickstarts check $F00000-$F7FFFF for a "Diag ROM" signature during early startup.
That is how the CS060 (and I expect all other 060 cards) can run with existing KS versions - there is a small ROM that has a snippet of code that fixes the FPU so it doesn't throw exceptions and continously resets your machine.
All you need is to make sure the addressing reaches your ROM which might need some Gary or other chips prodding. Then you have another 512M that will be scanned for OS modules just like the regular ROM at $F80000. IIRC - it's been a while since I looked at the gory tech details.
