Play in the rear differential

[2x_Tom]

I picked up a 71 k10 4spd this morning. When I drive it I get a kind of band noise with a high pitched ping if I don't baby the gas and clutch from a stop, a shift, or letting off the gas.
My first though was U joints so I went under the truck and checked the rear drive shaft. It has play but the joints are tight. Problem is the shaft spins quite a bit, maybe an inch of rotation before it locks up. I'm thinking this is certainly my problem, the clunk then the ping from the driveshaft as it engages. Any ideas what I should check in the rear?

[Grumpy old man]

Sounds like your spiders and carrier need a little inspection ,cheap and easy pull the cover and give it a good look while turning the wheels on jackstands depending on mileage and use it may just be time for a rebuild ...

[5150.4.67]

X2.... I had similiar issue. Pulled cover to find severly worn spiders. Rebuild shall result in another 40 years of service.

[Grumpy old man]

I just replaced my carrier in my 1995 GMC Z71- 3/4 -4x4 ,All the local parts houses here wanted $750. to over a grand just for the carrier (gov loc 80 ) went to ebay and found a brand new one for $299.00 + shipping I reused the ring and pinion new bearings and seals and she's perfect and ready for another 225,000 miles ...