The 12 bolt is going to hold up fine. It's only going to spin one wheel, but it's not going to break. If you do a lot of one wheel burnouts you will burn up the differential gears and the cross shaft, so I dont recommend it.
The truck 12 bolt did come from the factory with a Eaton Posi in the early '70s, but the case on those was weak and would crack. The new Eaton Posi for the truck 12 bolt is very strong and I highly recommend it. Tom's Differentials probably has the best prices on these, so contact them for the parts you need.
There are no thick gears for the 8.5 10 bolt to allow you to use the 2 series differential. The only option that you have with the 2 series is to use a spacer. I do not recommend that. I have seen the results of using ring gear spacers. Some people get away with it and others don't.
All of the 8.5 truck rear ends that had the limited slip differentail had the Gov Lock. Only the car 8.5 got the Traction Lock differential.