Ground and the first bit (B&W) would be on the A/B<->CRT Cable, but probably not 5V . . .

. . . leaving the possibility of one or two bits of addressing(?) from the 68000 bus on the interface . . .

. . . that'd mean at least two bits/four level gray . . .

. . . maybe four bits//eight level gray :?:

Dunno, it's a WAG-n-a-shot in the dark. :-/