right - but the beauty of doing the heavy lifting in simh is that you add/drop virtual devices as needed.   Make one disk with the VAXstation bootstrap and another with the 780 style.  Once you know you have a proper bootstrap, root partition, and /usr partition that will work properly on the target / you know that now have the bits you need to boot to 'single user.'  If you are really aggressive, you can create /etc/fstab.780 and /etc/fstab.vs before you go to the real HW.   Because the key point is the simh 'virtual disks' are just blocks and dd is your friend here.  You can build up the bits on the real disk from the known pieces you create separate files for simh.     Once you have a physical disk with proper bits boot, then start up to 'single user' and fix up anything that really needs to be HW specific.   Although a little work in /etc/rc{,.local} can even be pre-made to automate that by having the script detect with CPU you booted and ln /etc/fstab to the proper one.

As I said, you should be able to do almost all of the work on the simh system before you go to the real HW. 

Sure beats how we had to bootstrap systems back in the day.  The truth is we used pretty much the same process to do this type of task, but had to find a common disk between the 'parent' system and the 'target.'     simh can make Frankenstein systems that never existed in which adds a layer of ease, plus you even without that, since its just bits, you can take a partition from a virtual disk on any geometry and move them to another disk with a different geometry -- something much harder to do with real hardware.    Everything here is just SW, which is a load faster and easier ;-)

Good luck,

Clem