Seems you've been very thorough. I've seen many reverers sieze up 10 minutes after a "rebuild" when done by the wrong person. Most of the mechanics at the last Deere shop I worked at were not allowed to work on reversers, HL-Rs, or Powershifts. Just me and one other guy did those jobs. I guess we were the only two willing to read tech manuals and use a dial indicator.
18 PSI of lube/release pressure is plenty. It isn't going to be your problem.
In regard to outside tabs on your steel separator plates? You lost me. Maybe my memory is a bit off but as I recall, the steels have inside tabs. It's the clutch discs that have teeth on the OD. The old ones like what came OEM on 1010s and early 350s were some soft of bronze material on the clutch face. Later ones used some sort of thin fiber friction surface. All clutch discs had flat drive-tangs on the OD and none were twisted or bent. What you describe (clutch drag) often happens when a few discs or steels are warped. I'm wondering if you've got a few that lay flat when cold but warp a bit when warm? To be honest - we never reused any of the old discs. Dealer policy was always to install new ones. So my experience of putting the old bronze-faced used ones back in is almost nill. I have a 1960 1010 with a great working reverser that has never been apart since new. Just lucky, I guess. Mine runs 15 PSI on the lube port when warm and 95-105 PSI on clutch pressure.