Steve,
I don't know about being the "go to guy", still learning myself, but I've have learned that the 6 Cylinder world is very different than the 8. What surprises me is the difficulty of finding parts considering that so many were produced. I guess most are more interested in V-8's and imagine that the 6's and all their related parts found their way to the crusher more easily. I personally don't care either way; they're still Mustangs but that's me, not everyone thinks the same...and you'll never catch me dropping an 8 into a car that started life as a 6 or vice versa.
Anyway, I have the Differential completely disassembled now and am in the process of cleaning off all the grime and gear oil. All the Gears are in great shape but not so with the Bearing, Races and Seals. Found out that the Seals are the originals; paint still present. Something else I learned while pulling this apart; paint marks were also used inside some assemblies to indicate completion of a process; pictures to be posted soon.
The restoration has been great though, even if tough at times. It's also a bit different because this time I'm disassembling everything including the Steering Box, PS Pump, Alternator, AC Compressor and so on...you get the idea. It may be insane but I want to see how everything works and fix it along the way, even down to the Neutral Safety Switch.
I'll post pictures once done with the car. You and I have such similar cars, even down to the options, that it might be cool to see how close they are in appearance, even though yours is a Fastback...Grrrrrrrrrr! A Fastback!!! You lucky sap!
Ray