Finally figured out the geometry issue on the Chevelle. When I took it apart the rockers were hitting the retainers. Whoever put this motor together, ground metal off of the roller rockers, with a Dremel or something, in an attempt to get clearance on the retainers. Per the owner, this is the second guy that tried to fix the valvetrain problem in the short time that he’s owned the car.
These guys were exactly .080” off from getting retainer clearance and getting the roller tip in the center of the valve stem.
Turns out these retainers and recessed keepers are designed to be used with lash caps.
Neither of the last two techs installed the required lash caps.

I installed the caps and got the rockers and Trick Flow push rods in today. Valve covers are on and sealed.
I’m going to mount the exhaust tomorrow, make some 3/8” hardline for the brake booster vacuum and the PCV valve. Distributor is in, new plugs and just gotta run plug wires.
I’ll wire in the fan controller for the cooling fans tomorrow, too.