I doubt it's brazed...it wouldn't have needed swedged if it was going to be brazed.NO WAY it will slam out cold. The fork legs interfere with the slide hammer's handle for one. There's not enough throw either way.
Cleared the end very well before using penetrating fluid. Used a heavy steel rod from the top striking it with everything I had! Just laughed at me. I suspected so, worth trying tho.
It's probably just pressed with ~50 years of togetherness to overcome. It'll take a hydraulic press and the rod you are pressing with will probably need turned to ID of tube -.020" or so.
Drilling will be cheaper in the end if you don't have a machinist buddy. I wouldn't suggest it without a drill press, however...a hand drill with a big bit will take you for a ride when it grabs, and it will grab unless you are very lucky and go very slow.