Are there any tricks to removing the shaft from the companion flange at the diff? It hasn't budged with a couple taps of a deadblow. might just be rust or paint that glued together from the last time it was out. Just want to make sure before I start beating and prying.

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I don't know of any tricks. I have a '55 and it is "straightforward".
Pages 6-2 and 6-3 of the 1956 Oldsmobile shop manual says to remove the propeller shaft:
1. Remove four rear universal joint bolts.
2. Use a piece of soft wire or a heavy rubber band to hold trunnions onto spider journals and prevent loss of bearing assemblies when joint is disconnected.
3. Mark the universal joint trunnions and companion flange and then disconnect universal joint from companion flange.
Your suspicions are probably the cause of its reluctance. Just pry and beat with care so as to not damage anything.

 

so I pryed it off and it was fairly easy but the other end won't slide out of the transmission. there is a small screw on the slip yoke but I don't know if that is holding it on or what. I know on my '89 mustang the d/shaft slides out easily. this one is pretty well stuck with me pulling and yanking. any idea if the screw has something to do with it?

 

The "small screw" is a plug for a lubrication port. It was intended to be removed every 5000 miles and get lubricated with a special lubricant (567196) and then get replaced. In practice, it was often ignored, and the slip yoke suffered added wear. On my '55, I took it out and replaced it with a conventional chassis grease fitting. Then it could be lubricated regularly with the other fittings using conventional chassis grease. If you choose, you can install the grease fitting and pump in some grease. If it's never been lubricated it will take a lot of grease before it appears. That may be the reason it is currently "stuck". If you get some grease in it and "wiggle and pull" it carefully it may come out. Be sure to inspect it for excess wear before re-installing it.