With the robart 550's and not lowering the gear mount plates the wheels won't fit in flush (or the gear door wont be flush). You;'ld have to lower the mounting plates about 1/4 inch (give or take). I'm sure a retractable tail wheel would be a simple instal... The downside is the weight in the tail...Mine came out signifigantly tail heavy with the stock setup.

here some pictures of how much they stick out...

On another note, I've pretty much finished getting my RB ready to go again... (Gear mount folded on a perfectly greased landing on asphalt after a hand ful of flights)....the blocking i did for the gear rails will make it bomb proof....the wing will rip off before than damn gear rotates.

One thing i'm still a bit concerned about is cooling for the engine..... Anyone have any issues ???? My ys 140 is pretty much enclosed except fot the valve cover.... and the spinner sure does block off alot of the intake (allthough i suppose it has a ram effect on pushing air in)....any thoughts? On my last flight it sure seemed like my ys was overheating, but it's also a new motor and haven't gotten it perfectly dialed.