Borgeson steering coupler.

What do you think about losing the sliding action with swap of the factory coupler to the universal joint?

No good, as it needs to be able to slide somewhere. Just make sure it's not completely rigid. Some people just leave one of those set screws loose, although I'm not sure of the layout in your case. If the car is a newer B body with a rag joint, you may be good.

Getting ready to use one , and had not thought about the lengthening and shortening of the shaft as the joint makes its arc. Would knocking the plastic plugs out of the steer shaft and lubricating it work?

Using one in my 'Cuda. My life hasn't changed from losing the slip, from what I can tell...

I've used a Borgeson u-joint on my 'Cuda for 15+ years. No problems at all.

http://www.borgeson.com/mopar_action_borgeson_steering.pdf

Seems like Rick Ehrenburg did an early install and mentioned a few concerns. So Borgeson came up with 2 additional items. Return hose nipple and a sliding coupler.

Borgeson didn't come up with crap.

Peter Bergman did and he hangs out here, you'll see him a lot in the handling forum.