I worked on a 1953 No. 12 that had a siezed support bar. The first thing you want to do is get it to rotate, that way you know you've broken the rust free. I used a HF blind hole puller to get the split-cotter clamp apart:
That lets you get penetrant into the clamp area. A 50-50 mix of acetone and automatic transmission fluid works about as well as anything, Kroil included. You want to make sure the blind end of the cotter clamp is free. Put the clamp bolt back in and tap on it to break the clamp free from the bar. There are two split cotter clamps: one horizontally in the front, the other vertically in the back.
We were able to use the overarm support casting to break the bar free, using a dead-blow hammer:
Just some light blows until we got it broken loose and rotating 360 degrees.
Then we used some light blows against the back of the bar with a wooden block and sledge to tap the bar forward. We were NOT beating on the bar, just controlled blows to impart some momentum to the bar, with the sledge held as shown with ONE hand.
It was a process of me rocking the bar side to side and my buddy tapping on the end just enough to get to slowly move.
As far as a setup to press the bar out, I would rig up something that uses two lengths of 1/2" all-thread. You can get a 10 foot ong piece of 1/2" electrical support rod from home depot (in the electrical department) for about $10
link. Make a rectangular structure that fits around the bar, bearing against the front of the ram and extending beyond the machine on either side. Put beam of some sort across the back end of the bar and connect either two end of the beam to the box with the all-thread. Tighten the nuts alternately until it moves. A box and beam made of 2x6 lumber on edge might be enough to do the trick if you add some steel plates to distribute the load where the nuts bear. If you can't picture what I'm suggesting, holler and I'll draw a sketch.