My clutch has about 20k miles on it, installed new about 3 years ago.
Recently it has been hard to disengage. I have to stand on the clutch
pedal and push it all the way to the floor to get it out of gear.
This is rather scary when I expect to shift to neutral and the
vehicle keeps going. Once in neutral with the clutch all the way in
I could hear the tranny turning.

I quick inspection of the linkage revealed nothing obvious.
The adjustment nuts are in the same place as always.

The pedal starts to hit the friction point about 3" into the pedal stroke.
I suspect it's out of adjustment, but before I go moving the
linkage adjustment nuts, any other ideas? It's like I need another couple inches of push to get it fully disengaged.

That's what it sounds like, but it's not a typical thing. I would be looking for worn parts in the linkage myself...

Is it the hydraulic type or the mechanical type?

It's going to be the mechanical type here. It's an '84 model, and he mentions looking at the adjustment points.

That is what I suspected, but just wanted to be sure. I agree with Sierra.

You need about 1 1/2 inches of free play pressing down on the clutch pedal before the throughout bearing contacts the pressure plate fingers. If you are going down further before bearing contact, you will have less release of the clutch.

Just a thought and probably not the case here, but I had a similar issue with mine a couple of times and I found that the pivot ball for the clutch lever had backed out of the bellhousing and had cocked diagonally in the hole which gave me the same results. First time I just straightened it out and screwed it back in tightening it up and figured I musta just been loose for a long time....then it happened again less than a year later. Locktited it that time, hasn't come loose since. Just a consideration.

Well my clutch arm (sticking into the bellhousing) has a little play up and down, but not bad. About 1/4" back/forward play until it hits the pressure plate.
The linkage needs new bushings, about 1/2" of slop in various areas.

My friend helped me adjusted the threaded rod nuts just about to the end and the clutch is now working better. Sadly it engages towards the top of the pedal
stroke and not lower like it used it.

Feels like time for a new clutch soon. I thought it would last 100k miles, but
that may have been wishful thinking.

You need a new clutch when it begins to slip, not on where the clutch engages. It should be adjusted as I indicated above.