Aren't VAXen similar enough to where you could drop the -300's disk in the -200, install VMS (or dup from the -200's system disk), reinstall the disk in the -300, key in the -300's licenses and AUTOGEN? I don't know as much about VMS as I'd like to, but I've had the disk from a 3100/76 up on a 4000/200 to test functionality, and is seemed to work fine.