I know some people still stumble on this thread while searching the ether for brake solutions for their 1200. Good news is Doug is still responsive via email, and a pleasure to deal with.
A decade later, and I've got some information that hasn't surfaced in here just yet. These brake kits are also compatible with late model 1200 pick-ups with factory disc brakes. The late model ('89 - '94) 1200 pick-ups from Japan have 45mm strut tubes, and matching caliper hole spacing to the early B110's. Here's a photo of this brake kit, supplied by Doug, mocked-up on a late model pick-up.
The only modification required is the hub bore of the truck itself. The late model trucks have a 73mm centre bore, this must be reduced to 66.1mm to allow the S13 discs to slip over the front face. It's better to modify the hubs than the discs so that you can just use off the shelf parts time after time.
Clears *some* 13" wheels without a spacer depending on the barrel diameter immediately following the mounting face, as discussed at length previously in this thread. SSR MK1's, MK2's & MK3's will require a 5mm spacer because of their barrel design. Advan A3A's, Weds Racing MK1's, SSR Star Formula's all clear the B11/N12 caliper without the need for a spacer.