The cleat screws into the slide, I assumed the cleat-slid-screw combo held it in place - well, I'm sure it does. Problem is I was able to remove the screw (there was only one in the cleat) however the 'slide' does not slide.
I was messing with it when I really didn't have the time for it, but I did tap on it lightly with a hammer, enough to convince me it was not going to move easily.
My next step, I believe, will be to spray on some solvent. I've used heat before on stubborn bolts, I probably should not apply heat after solvent (hmmm).
If it's supposed to slide I'm sure I can make it slide

I was just wondering if it was 'supposed' to slide.
I said the cleat had only one screw. where the other screw should be is what looked like a pin (on the slide). It did not look like a twisted off or broken off bolt, but I suppose it could be. But even so, it should not be what is holding the slide in place, as there is no bolt head left. I'm not even sure if it is a bolt, I really think its a pin.
I looked on D&R and they have a downhaul cleat for a 22 that looked to be mounted on a slide. I would think even if it were stuck a light tap would free it. I suppose the if the mast were slightly warped or bent (it is an old boat) it could be bound in there, nothing a good couple of whacks won't fix, but if its designed to be fixed (as in tack welded in place) I don't what to be banging on it.
I just had a crazy idea. There is open mast track below the 'stuck' slide. I could get the downhaul cleat from D&R and slip it into the track from the bottom of the mast and let it rest up against the old slide. That would lower the cleat as needed. Is it possible this was the original setup and where my downhaul cleat is mounted is not for that purpose at all? The new sliding cleat would not even need to be secured in place, as it's upward movement would be blocked... I guess I need to see another 73 oday 22 mast to figure this out.
No, this won't work, the boom rests on the slide, that's the problem. I need some sleep. I'll go visit the boat tomorrow and figure it out.