I've got one that I'm using with a GVP HC+8, and it seems to work just fine with that. The BigRAM stays clear of the Zorro II memory space by default. I think your main obstacle to 8MB in 68000 mode is the memory soldered to the A2630. The documentation says that if you disable the A2630's memory, the BigRAM2630 no longer gets autoconfigured. And if you don't disable the A2630's memory, you'll have less than 8MB in 68000 mode. You can add the bigram tool to your startup-sequence
to initialize it when the A2630's memory is disabled, but I haven't tested that.