You do whatever you want for you locally, of course, but I'm 98.5% certain there is no hardware in the nimbus to detect when a Dx value is written to the command register address and insert a bus delay in that case. So that wouldn't be accepted as-is, unless you have a way to prove there is such a thing.
As for the interrupt, the bios uses d0. That's a "gentle" interrupt we're probably running as too harsh, it's d8 that forces immediate stop. So I think we need to let the current action complete if it's a read or a write (not a search), which would probably do nicely with the rmnimbus.
The timing changes, otoh, why do you need them, what is happening in the bios?