The R-4 loaded should just stand on its own, at least mine do. Has not been a problem to handle them alone.
You need to rotate the pin (flat part on inside that bolt went through is attached) about 90 degrees back then it slides out to the inside. I have to take mine off on 3520 to put backhoe on. Never had a problem; slides pretty easy. If it is not rotated it will not move.
I guess another option would be to visit the local auto parts store and rent a ball joint press. From the looks of it, the press should fit around the frame, but I'd measure before you bring it home just to be on the safe side.
I agree with yooper68, that if the keeper bolt is out (and you said it is), then rotating that pin by a flat bar or large screw driver is the best way to get it broken loose.
Hitting with a maul or putting pressure from a bottle jack may just break a casting. THAT be expensive...
Interesting that that pin LVU15084 lists for around $25, except Sears has it listed at $94. Same part no.