You'll find that MANY of the 19" monitors are
optimized for odd formats.
This is particularly true of DEC monitors. In fact, DEC seemingly made
certain their monitors would be totally useless for anything other than
their intended application by choosing some odd geometries e.g. 1152x831,
The idea is that you have to use a REAL DEC monitor on DEC, not that you
can't use it on other stuff (which they could give a rat's rear about).
The card was a Photon board with a customized BIOS ROM
that made it work OK
Macs are way easier to get working with the weird monitors. For the PC I
have heard good things about the Matrox Mellenium G200 cards, which I
"think" are highly programmable. The real catch with the PC is supporting
the DOS startup modes at some faked variation of 640x480.