Vigra VS-10 hardware docs, anyone?

Digging through a box of SBus cards pulled out of storage, I found a
card marked "© 1991 VIGRA, INC.    VS-10 REV B".  It's got a back panel
with four switches and a DA-15 connector.

Poking at it with the console FORTH in an SS20 made it look like a
framebuffer.  So I de-tokenized the FCode and, sure enough, it is.
I've got it working enough that I could probably build an X ddx layer
for it.

But it involves a lot of magic numbers.  My current code reads like

 set_g300_reg(0x4a0,0x800);
 set_g300_reg(0x4a4,0x198);
 set_g300_reg(0x4a8,0x0);
 set_g300_reg(0x4ac,0x1e3);
 set_g300_reg(0x4b0,0x1d);
 set_g300_reg(0x500,0xff);

I know it's a long shot, but I'm wondering if, by any chance, anyone
knows where to find hardware documentation to help me turn some of
those magic numbers into something a little less cryptic.

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