So here's the backstory:

I have a 1954 Chevy 3100, which had a 235 in it. I swapped the 235 for a good running 230, and replaced the 3 on the tree with the SM420 (I know it has the same final gear). Before I put the 230 in, I put a new clutch kit on... disc, pressure plate, throwout bearing. Then it sat for 3-4ish months over winter as I worked on other things. I got the brakes sorted, got the driveshaft in... ready for a short test drive down the road... or so I thought...

I can't get it to go into any gear with the engine running and the wheels on the ground.

Engin off, no problem... shifts smoothly. Engine on, with the rear jack up... same thing... shift no problem.
Crawled under the truck to watch what happened when The clutch pedal was depressed. The throwout bearing comes in contact, and presses against the pressure plate, the pressure plate DOES release some of the pressure on the clutch disc, the clutch disc doesn't come off the flywheel at all. I CAN see some movement between the two layers of the clutch disc.

Its almost as if the clutch surface has frozen onto the flywheel over the winter?

Throw some ideas at me!

Clutch disc turned around? Wrong throwout bearing? There is a long and a short.

Clutch disc is the right way. Flywheel side against the flywheel. I suppose it COULD be the throwout bearing. The one that's in it now does engage the pressure plate after about an inch of pedal travel and I can see it relieve some pressure on the disc

Could be rusted to your flywheel. Get a helper to press the clutch pedal all the way to the floor with you underneath with a thin putty knife and work the blade between the flywheel and the friction disc.

This has happened to a number of my old trucks that have sat through a winter outside during the rainy season.

Being inside I wouldn't have thought the clutch would have rusted to the flywheel... but it had. Thanks for the advice Ken, I didn't do it that way, but you would have been right on the money!