Nice hammer Toolmaker. I built a Krusty style years ago, was never happy with it. I later acquired a Clay Spencer tire hammer, the original owner was upgrading to an Anyang air hammer, and have gotten very good service out of it. Since I wasn't the original builder I did have to go over a couple areas that the welding could have been better. Very good control, hits hard and fast. I don't know if Clay still does classes, but it used to be about 1200$ and a week long build and you went home with a new hammer. Check out ABANA, you might be able to contact Clay or get plans from there. The toggle linkage is basically a copy of the Little Giant toggles, with a doughnut spare tire as a clutch. A buddy of mine built one from the owner's manual and used a trailer tier instead. If I was to build a new one I'd probably design the tire at the back and the counter weight in the front run through pillow block bearings.

Another interesting build is the X1 on Anvilfire.com, they never came up the X2 version or plans, but there's enough info there to plan and build your own.