John,
I have an observation regarding your UHMW guide blocks. It appears in a brief glimpse in your video, that your adjusting/locating screws for the UHMW blocks have pointed (conical) ends, and conical holes. I could not see if all of them are such, but if so they could possibly be the reason you are not having as good of results with your bearings. As the tup goes up and down, the bearing blocks have some friction, that would make them want to move up and down some also. The conical points and holes would act as ramps, and tend to push the guide blocks harder against the steel surfaces as the tup moves, increasing the friction as it moves, making proper adjustment difficult.
If your adjusting bolts had cylindrical flat bottomed ends and bores, they would locate the blocks, and allow adjustment without tending to increase the pressure on the tup as it moves up and down. Just a thought, but it may make a difference.
I think set up right, that the UHMW should work quite well, and be durable and forgiving. Make sure that what you have is real UHMW, and not just high density polyethylene. UHMW is a sentered material, made from powder fused under high pressure, and has the ability to retain a little lubricant. You can also adhere it with epoxy successfully, if you flame treat it first( run a touch over it briefly ). It is the material used on the bottoms of snow skis, snowboards.
Your hammer is beautifully designed and built! I enjoyed your videos a lot!
Best regards,
Ron