I was told that there were very few options for replacement ring and pinion sets for a 3/4 ton rear end.
The frames are very similar on all K20s up to '87 so adapting parts from that new isn't real hard.
It isn't so much as ring and pinion are hard to find for that rear, its that the only set anyone really wants is rare as hen's teeth.
Three ratios were available, 5.13, 4.57 and 4.11 (I may be slightly off in each of those), but the one people usually want is the 4.11 and few survive.
