A couple things..
T6/P51 tow bar goes between the main gear, and I have hooked/unhooked,pulled and pushed many of both (I ran ground ops at airshows, and don't own either)..they are no fun, require 2 people and can wreck things if mishandled...made me a nervous wreck every time I moved one. I can't even imagine using one on my RV-4, especially at the tiedown points. You would have to slide it in place, crawl under to safely hook it up and remove it. Now, there is the guy in Fla with the radial RV-8(painted like a Grumman Wildcat) that made a period correct towbar for his that fit to the inside of each main wheel, and it's really cool. Look him up and copy his idea.