be careful with the hammer don't want to break anything. a c-clamp works great but you have to have one large enough to place a socket on one end the same diameter as the cap or little smaller and on the other side you need a large enough socket to allow cap to fall into and place the c-clamp on each end of the sockets and tighten if it gets to hard to turn c-clamp use a boxed end wrench on the turn pin for leverage....and 4 sets of hands ....goodluck.
its really easy to do if you do it in the grass. if you have a nice soft grass spot just put the end of the driveshaft over that and use a socket and hammer. pops right out and no worries about breaking anything since the ground will give much sooner than the driveshaft or the yoke
I have done it both ways (I do U-joints with the DS on the car, so I preface my post with that perspective). The 4# hammer works fine if the caps are moving easy. I really like the C-clamp method though, and once the caps start moving, it doesnt take long for them to pop. I have bent a couple 6.5" clamps doing this - the industrial C-clamp in my ball joint press tool kit is much beefier and would work a lot better.
If you have zerk fittings on the new joints, install them correctly (there's a strong and weak side - this is a nuance not many people bother with, but why not do it right).
I will try my bent C clamp again. If I can not get it off, than I will rent a ball joint press from AutoZone. I am buying the brute force brand U-joint without zerk fittings.