Well, we pulled the top of the engine. What we found was 10 of 12 push rods that were less than perfect, and 12 of 12 bad lifters. Both the lifters and the push rods on #6 were in deplorable condition. So, we replaced the 10 push rods and all 12 lifters. That was the second bad set of CompCams lifters, so we used GM Performance lifters, this time.
There was some slack in the shift cable, so we fixed that, and also adjusted the cable for the shifter. I still can't shift to first, but we ran out of time.
Tomorrow, I'll run by Medina Lake for a shakedown run. That should be about 2 hours' of driving, all told. Then, we'll replace the left axle, and fix the dust shields. I hope to address the grounds, a few dead circuits, some fluid leaks, and the non-op check engine indicator, as well.