Agreed that the differences weren't much between the 66 and 86 trannys and rear ends, sorry that I implied otherwise.
As far as the 3 speed, that was because the 15's used a much bigger rear end only allowing the use of three gears instead of 4? That is my understanding anyways. I've heard it's tough to keep a rear end in a 1486 due too the higher horse power.
Casey in SD