I had a similar problem with my SX/4. The clutch would almost disengage with the pedal all the way to the floor. I would have to start it in gear to be able to drive it, and even then, it was difficult to get it into different gears.
I thought I had air in the clutch hydralic line, but could not fix the problem with repeated bleedings. Turns out that the clutch pivot ball was missing. Last time the trans was out, it must have fallen out. With the ball in place, the clutch was only slightly better. It still didn't work properly, though. Nest was to rebuild the master clutch cylinder, then the slave cylinder. After this, it still wasn't any better. I then put in new master and slave cylinders, but still no good. The hose that connects the master to the slave looked to be in great shape, but that was the only thing I hadn't done anything with. I figured that had to be the problem, so I pushed a piece of grass trimmer plastic line through. From one direction it went through, but from the other direction (from master to slave) it did not go through. I cut open the hose and found the inner rubber liner loose. When low pressure, like when bleeding, it was fine. But at high pressure, the inner wall would collapse and plug the line. I guess I should have suspected it earlier, since I know that rubber gets old and deteriorates with age.
At least now the whole clutch system is fixed and renewed for the next 30+ years.
I should add to the story that the missing clutch ball was cause for removal of the transmission, which led to a rebuild of the tranny. The 1st and 2nd gear syncros were worn. The brass syncros had wear, but it didn't seem like that much. The tranny shifts much smoother now, and I can downshift from 3 to 2 without problem.
That was my clutch ball story.
If anyone need clutch balls, I have some spares. Just send me a message.