The service manual is one thing, experience is another. And there were two questions and I doubt the service manual covers welding on new perches. But I'm thick-skinned, I can take a bit of sarcasm.

So thanks to those who provided helpful replies.

The rear end is a '69 B-body unit. Apparently low milage and in very nice condition and complete including drums and cables. Originally 4.10's but now 3.54's, The cover would definitely come off eventually but I'm no rear end expert so unless the gears are chipped to hell I wouldn't know what to look for. I'd rather avoid a complete teardown for the sake of welding on a couple of perches but I'm pretty sure the axles need to be pulled to swap the studs. In fact, I just looked and they are the original RH and LH threads !!!