As you may already know, you can pour a solvent into the clutch which may penetrate the corks and eventually free them up. This is a process that takes several days, and you rotate the clutch each day to make sure that the solvent spreads around to all the corks. Meanwhile, you would depress and release the clutch pedal from time to time. Usually, it works without the necessity of surgery.

Someone will jump in here with the recipe, shortly.

Many people force the clutch pedal to the floor with a stick, over the winter when the car is not being driven, to prevent sticking. I guess I'm lucky, for in almost 50 years of ownership I have never done this, and have never had a case of the clutch sticking after the car had sat unused over the winter.

As Jon pointed out, make a stick/prop long enough to depress the clutch pedal, using the edge of the dash to prop it from. If the clutch had been replaced somewhat recently before you parked it, the clutch fluid should be clean and not require to use solvent blending to break it loose. Just prop the pedal, turn it over for a few days, maybe even warm the engine up each time, should expedite it coming loose.
If it wasn't replaced, and you don't know the integrity of the clutch assembly, then follow the numerous discussions using solvent mixes and procedures on this Forum.

Gentlemen Thanks very much for the tips. I'll look further on the forum for the solvent mix.
John

John,

Since you have the engine running, here is a procedure I have used successfully:

1} Support both rear wheels on stands, so the tires are not touching the ground, and the handbrake is off.

2) Start the engine with the car in 3rd gear.

3) Bring the engine speed up to about 30 miles per hour.

4) Apply the brakes suddenly.

This usually frees the clutch since the engine is going quite fast when the driveshaft is suddenly stopped.

Only do this in 3rd gear. Doing it in another gear could damage the transmission,

Per

Thank you very much Per. I think, though, that I'll try the solvent solution first.

John

Gentlemen, thanks again for your input. I did get the clutch plate unstuck, using sort of a patchwork of your suggestions and one from my brother in law. I depressed the clutch pedal with a 2x4 propped against the under side of the dash board, and left it there for about 3 weeks. Then I jacked up the right rear wheel, put the car in third gear, (engine not running) rotated the wheel, and the clutch plate came loose. I'm going to leave it on a block for a few days, rotating it once a day or so to be sure that the clutch fluid (assuming there is any left after 43 years) washes over the plate. I plan to drain and refill the clutch fluid before driving the car, again assuming I can solve the seized clutch fluid plug issue.
Happy New Year to all!

There is only 1/3 of a pint of fluid in clutch. I doubt it "washes" over the corks just by turning it.
Imperative that you get the fill plug out.
First, i would pull the fill/drain plug while in the bottom position. Then rotate into the fill position above the starter and put in new fluid. Start the car up and the oil will "sling" as the flywheel spins around. Work the clutch pedal back and forth as the car is running. Do this procedure several times a day for a few days and the corks should be coated.
Also hoping the corks were not torn during the unsticking process.
.

Thanks Kerry, I'll try that once I get the seized up fill plugs out.
John