In my QEMU fork there is support for a 68000 virt machine so you can have a multi-ghz emulated 68000 with 128MB RAM (maybe more, haven't tested) if you really want that.
N.B. The Author of Chip4Mac68000 has been planning a port of uClinux in the future with his SDK which explicitly avoids using the Macintosh ROM at all, running bare metal directly on the hardware. Might be worth taking a look at if you're unfamiliar.
I'm going to do a u-boot port for the Mac at some point. It'll use the ROM to get loaded and then get rid of it. That'll work on nommu and mmu Macs and make the modern linux on Mac experience a bit nicer.