Sorry, I don't have my Capt. Crunch decoder ring with me. I will try to do what I can.
Passenger side tube will have the 2 letter code stamped on it. As for stock gears, most of the time they stopped at 3.91, but a few rare ones had the 4.33's. You could go higher but, those were dealer installed.
Those were Olds only rears. They will hold up if you are using treaded tires, but if you use slicks with them, they will show their weaknesses.
If you have a '68 rear, if it is a 3.42 or steeper it will have 31 spline axles. Otherwise, they are 28 spline. An oddity for certain.
If you are looking for parts, I have the name of guy who rebuilds these all of the time. The new richmond gears that are available require the carrier that was for the taller gears (my brain has lost that 3 number code?) You can go to Reider gear and they have new posi units that are reworked Ford setups. Or you can have some fun, you can get a Richmond gear Lock-rite locker for an 8.5" GM axle and it will slide right in. It has a little noise, but it does the job!!!!
Casey Marks built the one that I have under my car right now. The 3.9 richmond gears are a little noisey, but I don't really care under full throttle!
