Since I originally posted this question, I built one for my long guns and even made it to the range once to try it out. It had a couple of issues, one being too tall in the front for that particular range at 100 yards, the other was the front adjustment, made out of a 5/8" stud bolt had a small wiggle which magnafied into about 2 inches in 100 yards. I have since re-worked the adjustment but still need to address the height. Next time I go home and if I get the time, and can remember, I'll try to take a couple of pictures to post. I built it all out of scrap I had including a wheel from an old scooter and parts from an adjustable bed from Ikea. I shot several rounds from a 30-06 and at 100 yards it stayed within a 2 inch circle, but I really expect to get less than a quarter size pattern once I get all the bugs worked out. My goal was to clamp the rest to a fixed shooting table, clamp the rifle in the rest, adjust the scope to the bullseye, fire, check to ensure the scope is still bull's eyed, then adjust the scope to the bullet hole and repeat.
Oh well, with work and the Son going into the Air Force soon, it may be awhile before I get to tinker with it again!