[Yukon Jack]

The Rockwell T221 was used through the 1969 model year. My 69 K20 had a Rockwell T221 married to a manual three speed. I have since changed to a SM465. I have a spare Rockwell T221 and SM465.

There aren't tons of these out there but not exactly rare either. Hard to get parts for the Rockwell, but you still can get some stuff. The adapter can be hard to find.

The Rockwell + adapter + tranny is the same lenght as an NP205 + adapter + same tranny.

The Rockwell is gear driven like the NP205 and has the same gear ratios. Just as strong, just older IMO. If you tear yours apart, make sure the spline coupler is in good shape, they can wear out.

The couplers are hard to find at a good price.

When I did my swap to the SM465, luckily I found that I could have the existing one cut down to the correct size for the adapter for the SM465.