Sheared the keyways side ways on my transaxle and shifter stuck

Hey guys i got a 6spd spicer 4360 or somethen like tht i like the transmission but my mud tractor has been sitting since its winter and im snowmobiling not tractoring but i started it and my shifter is stuck. It wont shift unless u use 2 hands and u can pull the whole tractor sideways the shifter is locked so hard..i know i need to take the tranny apart to adjust and grease the shifter keys and that little ball bearing thing but the problem is i have to take my 27" atv tires off to get it off and my keyways are sheared like they wedged themselves completly in on a angle between the rim and axle and the rim wont budge on or off...what should/can i do about that? Thanks

flip it on it's side and remove the trans with the tires still on it. a quick run to anywhere that has a press is your best bet. It's that, or cut the rim hubs and replace the rims. 27 inch tires are a LOT to ask from a small keyway... maybe while you have it out you can cut the shaft for a bigger key (rims will need the same key cut in the hub.)
Ideally, you would have shaft and hubs splined.

Was your shifter like that when you parked it? If not, one of two things has occurred: Water ingress turned to ice and she's frozen, or rust got the better of things and jammed it up that way. You could try putting a halogen lamp underneath it for a few hours to see if you can defrost it...

ditto on the splined thing most of your heavy duty tractors have splined axles some are splined and keyed lol