Jeff,
thanks for the confirmation. It's been over twenty years since I did that and the memories are drifting back, so for what it's worth:
a vendor sold me a t19 from a Scout that had hidden cracks. I picked up a t19 from a 2wd at a pic'n'pul for cheap. The cases were otherwise identical except that on the passenger's side of the case, there was a boss that for some other type of application would have been tapped to mount a bracket of some kind. The front bearing retainer on the d20 would clearly not clear this boss, so I ground it down almost flush with the case and got the clearance I needed. Also, there was another boss that cleared everything but had a tapped hole - so I retapped for a pipe plug and plugged it. So there clearly are Variations in the same basic case, depending upon final application. Jeff pointed out variations in the d20 front bearing retainers. So one could conceivably have the interplay of two "variations" at work that could momentarily stop one in their tracks, until they pull out the grinder!
Regarding drilling/tapping a 2wd case for a 4wd application. Some of the holes that hold the 2wd bearing retainer in place line up with their 4wd cousin. So you put a bearing and snap ring in place, and bolt up the 4wd adaptor with those bolts that line up. Accurately center punch the needed holes, drill and tap, and then plug the 2wd holes that don't line up. I put gobs of miles on that case and pulled a trailer through off-roading trips, so one shouldn't shy away from adapting a 2wd case if need be.
