I'm pretty sure that a VS3100-76 with no graphics board *will* come up
using onboard monochrome (use the green signal).
I don't think I've ever actually used one this way, but I do
know that the GPX and SPX options came with a little stick-on
panel that said either "GPX" or "SPX" in about the right size
and font to stick right after the "VAXstation 3100 M76" nameplate.
Mine does and it is just a matter on which pin you pick it up in the
back of the box! I'd have to go to my office to ck it again.
Fred