CP/M on Vax
I'm late to the party here but for posterity this was implemented by plugging a real Z80 card into the VAX11/780 backplane and there was some magic to route disk and console support out to the VAX and a users terminal. As I recall we could afford 2 of them and they had to be shared.
I can only assume we did that because the Tektronix cross assemblers that we used on the VAX for the QL development didn't support the correct dialect to be able to assemble the original source code. At the time Tektronix did a range of cross assemblers but they all shared a common set of directives that likely as not were not the same as the original processor manufactures assembler.
The only other site in the UK that was using these boards at the time was some defense contractor down Southampton way, that was just far enough to justify the use of the SRL twin engine turbo prop for the day trip from Cambridge to go and see them in action. Normally that plane was used for the monthly (possibly weekly) trip to Timex in Dundee to try and resolve manufacturing issues.
Different times.