Hang on fella; 413 said
65 and newer AND ALL SURE-GRIPS, use the 1.5 T-bloc.
So all you need to do, is swap into the old open diff, is a later bloc, or just install a second Sure-grip.
Or do what I did, just weld a pair of hardened washers onto your skinny block until it gets close enough to work with your adjuster. Unfortunately, the whole thing has got to come apart to get the block out, IIRC.
Hey I just noticed that you are in Grimshaw. Is that Grimshaw Alberta? you are only 18 hours from me, and in the same country. I got an extra refurbished cone-type SG here ....... with a 1.5" block already installed. And I have some spare chunks here from 2.76 to 3.23s that I could install it into................ but no spare long T-blocs