This has turned out to be a case of several small complaints that add up to a hard shifting transmission. I'm glad I have gone to the trouble to pull the gearbox and have a look.
The clutch disc was definitely worn to the point where the wear indicators are barely visible.
The release lever was not properly secured to it's pivot and I don't think it ever was because the wire clip was just laying in the bottom of the bell housing. There's no way it could just come off completely. It may be the case someone was in there before me, took it off and didn't replace it but I truly believe the transmission has never been out of the car before this. I've never seen one that was as hard to remove as this. Everything that could offer resistance, did.
I don't believe that the fluid has ever been changed either. The drain plug was damn near impossible to remove. In fact, I didn't get it or the fill plug out until just about an hour ago with the transmission out of the car. I'd used PB'laster on both over the course of several days, tore the hell out of the hex heads on both and ultimately had to start them out with a hammer and sharp chisel.
The rear seal was leaking, too.
New seal, surfaced flywheel and new clutch are installed. I will be fixing the release lever and installing a new bearing after I get some lunch. I'm also going to call the Volvo dealer and see about getting the drain/fill plugs. I might be able to find a cheaper replacement for the fill but I want that magnet on the drain.
So many small problems. But it will have been worth the struggle when I get all this straightened out, cleaned up and reinstalled. It'll probably be tomorrow before I get it all back together but I see light at the end of the tunnel.
Thanks, everyone, for all the input. I may still have questions but I think I've got this in hand.

Addendum:
Volvo dealer sez $13.73 ea for the plugs. $1.43 ea for the copper gasket. Ouch! But I gotta have the plugs. No way am I using the old ones. They are too manled at this point.
I'd already checked the old gasket against one for the oil drain plug and it's ever so slightly smaller. They have to order the plugs and won't get them until Friday. Should have called earlier since I knew I would need them.
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'80 DL 2 door, '89 DL Wagon