I'm guessing its a Chevy, not a GMC since you said it has a 292. I have a '69 GMC, and it had (originally) a 350/sm465/rockwell t221/closed knuckle drum d44/d60 rear (30 spline). I *believe* the only engines available for 4x4 GMC's in '69 were the 305 V6, the 307, and the 350.
The Chevy's seem to have the Eaton instead of the D60.
The Eaton rear is strong, and I believe superior to the 14 bolt in a few areas. However, the bearings for them are pricy, and so is the brake stuff. BUT, you can get disc brake brackets for these axles.
The Rockwell T221 IMO sucks. (Mine exploded) Because they are so narrow and tall, you need to check the lube level frequently or the input bearing will seize up (wreaking all kinds of havoc). NP205's do not have this problem because they are short and wide instead.
They also have the same weak 10 spline drive sleeve design as the early SM465/np205 combos.
Rebuild kits are available for these, as are all the bearings and the seals, from the parts store.
If you want a PTO for one of these, good luck (unless you have one). They have a weird 9 bolt mounting pattern.
I think that if you kept an eye on the lube level, the rockwell might be a good strong case. The low range ratio is 1.94:1, so its a hair less than the NP205's.
no aftermarket goodies for this, either.