Anti lock brakes

[MdR]

Can anyone give me a good reason why it would be difficult/dangerous to modify/fit an ABS system from a production vehicle? :befuddled
I reckon a vehicle from mid/late 80s that ideally had no engine management as such & had ABS as a factory cost option would be the best bet. This (in theory!) would have an entirely separate ABS brain, loom, modulator etc. that I could rob & fit to a Beetle. I know that UK spec twin carb Honda Concerto fits this discription (might have electonic ignition).
I already have 944 discs/calipers on all four corners so fitting the later front ABS sensor ring would be no hardship. I figure the rear ABS ring could be fitted to the CVs or the stub axles (I don't know how the Porsche factory did it on 944s).
OK so 'sensible cars' are front engine etc. so weight transfer would be different, but surely all ABS does is sense the wheel(s) are locking & pulse that hydraulic circuit.
I'm aware that there are different ABS systems 3 channel 4 channel, split diagonal etc. is there anything else to bear in mind?
cheers
Martin :haveadrin