Some suggestions, since you haven't gotten any already.
Use the SIMH papers directory
http://simh.trailing-edge.com/papers.html
to learn more about VAX architecture and simulation.
An approach I might take would be to look at the
ka655 sources, the difference between the KA630 and the ka655 here:
"VAX Processor Chart", by Bob Supnik
http://simh.trailing-edge.com/docs/vax_proc.txt
And try changing the source. It Is Qbus BTW.
Maybe all this is what you've done already...
Thoughts?
Bob has published his email address. I would read up everything
he's published first (in part because it's not too much, I haven't seen
any books) and then if that information hasn't helped me already I
would then bring him my question. Don't want to waste that guy's time.
John A.