You can set a socket that fits just inside the shaft's diameter between the coupling on the transmission and the shaft flange as a first step. It'll take longer bolts, but you can do it with an inch of play.
Don't crank it down and try to break it loose, but put 20 foot lbs or so on each of the bolts. Just use a stubby 3/8's ratchet, or box wrench rather than breaker bars... Don't hammer on the transmission side of the coupling with the bolts attached, unless you want to install a new rear transmission bearing.
Hose everything down with penetrating oil
, and come back the next day.
Take a torch and heat the shaft coupling up until the penetrating oil
burns off, and spit sizzles off the shaft beside the coupling. Think 10 minutes or so of heating
. It helps if you can rotate the shaft over, and evenly heat the coupling.
Let it cool down.
Spray it with penetrating oil again after it has cooled down enough that you won't make it in the paper for self immolation...
Try to put a 1/4 turn on your coupling bolts. If they are just as tight after a 1/4 turn... stop. Loosen them completely and verify the socket has not slipped and is contacting the face of the coupling, instead of the shaft.
Tighten back down, and bring out the torch again.
I use map gas, on a torch with a flexible hose.
If you have clearance for a gear
puller, sometimes you can cut the shaft hose out of the way to slide the shaft aft. Sometimes in a pinch, a harmonic balancer puller can be put into service
... Though you may have to whack the threaded end down short enough to fit the space you have.
Heat under tension works better than a lot of tension alone...