Adjusting the radius is a darn sight more complicated, but is certainly possible. Here's how I'd do it. The screencast pics up where the last one left off. I did the arcs on one end, you can do the same mirrored on the other end of the block. You can then add the radius parameter to your block properties table and input the appropriate distances. The arcs need to be scaled to change size. The linework that connects the arcs also needs to be moved/stretched appropriately to clean up correctly. To explain my calculations, first I copied the pertinent linework. I then scaled it so the radius was equal to 1. I then copied the linework and scaled the arms to 2 (parameter change of 1) and adjusted the linework to the position were it should result. This then shows the distance modifiers and angle offsets necessary for the stretch actions on the specific vertices of the lines. See screencast.
