It would be a fair amount of work, but not impossible.
Depends on if you want 4 channel or 3 channel. 4 channel is significantly harder. And neither are easy.
Find a donor vehicle(s) in a boneyard. Prefer a 92-96 B/D Body (not 94-96 D), Get ABS Controller and motor (if not part of controller), probably master cyl, often they are different, as they have to supply fluid to the controller/motor resovoir, the whole rear axle (for rear speed sensor), front spindles/rotors for front sensors (are spindles needed or can they be modified for sensors?), wiring for them, wiring for dash ABS light, ABS controller will likely need vehicle speed input from ECM (hopefully it is compatible with ABS controller you have)
Easy? Well, not really.... But by the time you are done, it would probably be cheaper to get 92 that has it....
For 4 channel, you have to run a new brake line to the rear so it has 2.
I will dig up in my books and see what else might be needed if you are still interested.
Personally, I would look at getting an adjustable brake bias control. NASCAR has some brake line delay to the rear that helps, not quite ABS, but said to significantly reduce lockups