MIKE - Would probably help US help YOU if you tell US what all you worked on and had apart.
If you didn't mess with the reduction gears, didn't have the stamped steel cover off the reduction housing all must be well in there. IF you forgot to install one of the two roll pins into the driveshaft coupler, the driveshaft would push backwards when you pushed the clutch in. If you securely block up the back wheels of your tractor you can easily see the driveshaft and roll pins in the coupler from underneath the tractor, can even work on it if you like. Lots of work removing the fenders especially if you work alone.
I forget what Plow Day it was, was at Blunier's, in the spring, only PD I took two tractors to, my #72 and the 982 for SON. Had extra wheel weights on the 72, and the normal 3 sets on 982, I ran over a pile of bean straw, land wheel spun till it dug down to solid ground and "SNAP", front roll pin in the driveshaft coupler broke. Steve and BIG STEVE let me use their shop and attenpt to repair the tractor so I could continue plowing, even gave me a selection of roll pins to chose from, power tools, light, think there was even a radio in the shop. Working from underneath made it pretty difficult, I eventually pulled the tractor back to the parking lot and pulled the 72 onto the trailer and I let SON plow a few more rounds. When I got home, I unloaded both tractors, returned the rented trailer, and started right in fixing it again when I got hole. I syphoned all the gas out of the tank, removed the battery, and lifted the front of the tractor with my loader till the tractor was vertical, half hour later I lowered the tractor, replaced the battery, added gas and ran the 72 around the yard a bit. MUCH easier sitting on a low stool working on something about knee height.