You have to be kidding me. All you need is a 2764 and
a programmer.
It's a ROM and the pattern is in the manual, what could be easier?
Actually if someone were building I'd suggest using a 2764 over the
part used on the VDM1 as that was a two or three voltage part and
27C64(or even a 27C256) is common as flies plus lower power.
Well if I still had
the manual let alone the the VDM ... :(
Manual is on line I think at both Dave and bitsavers.