Ok guys, it's been a long day and thankfully it has ended on a much better note than it started on! I took my mangled pipes to a local plumbing shop and they put some new threads on for me which saved me about $40. I combined zz and bp's advice and came up with a fairly good solution. I took my T-post driver and welded an 8lb chunk of angle on the side of it, then welded a 3/4 x 4" bolt on the end so I could put another 20lb of cast iron weights on it so the device now weighs roughly 50lbs. I would add more if a machine was doing the lifting instead of me!
I decided to just use the couplings instead of trying to find another drive cap. After a few minutes worth of work, I stop and re-tighten the pipes and couplings. I drove in 5' of pipe with no problems in about an hour and it didn't damage the couplings or the pipe.
This method is pretty much what zz and others described except mine is lighter in weight and I have to "run" it manually (which is one good workout if you are in to that kind of thing). Even so, when I raise and release my driver, it strikes the pipe squarely and it has a much more positive feel to it. I lift it about the length of the driver and then let it fall, probably 18" or 2 feet at the most.
I'll post a picture of my contraption tomorrow but I just wanted to share the positive results of the advice I was given here earlier today.
