Looks good, nice job....
http://www.mytractorforum.com/showthread.php?t=56681The bottom edge of the blade has an angled piece bolted to it - so there is roughly an inch wide "bar" of flat surface for the blade to ride on. It worked fine on my other tractor. The trick is to mount it so that when the blade is lowered, the angled piece is flat on the ground.
If you don't get the initial angle (mounting) right, it will either have a tendency to dig in as you mention, or ride up over what you are trying to push.
If I do anything, it would probably be to raise the angled piece slightly (relative to the ground) and bolt a strip of UHMW (Ultra High Molecular Weight polyethylene) so the blade won't leave scrape marks on the driveway.
Oh - and I really like your 4-wheel wagon in your avatar. I have an old rusty white 2-wheel wagon that I need to clean up and "John Deereize". Got any up close pics of your wagon?