8.25 C-clip eliminators
The C-clip eliminators I have seen on GM cars are a total nightmare. My friend has a 68 Chevelle with a 12 bolt and it had C-Clip Eliminators, leaked like crazy. IIRC the bearings were kind of small also. He eventually bought new axles with Ford 9" Torino bearings and modified the housing.
I think for you, you can either use rear disk brakes (the calipers will generally keep the axles from sliding out), or install something with bolt-on axles like an 8 3/4.