I agree on the 10x5 for a .40 LA
Depending what you've had to pull apart already a tail-dragger conversion isn't bad. Move the main gear up (with suitable bracing inside - 45° corner strips on a 1/8" ply pad or similar) and get the axles about even with the leading edge. The tail wheel is always more work if you want steerable instead of just a skid or caster wheel. In the past I have done LT-40 and a Big Stik conversion to tail-draggers and in both cases was greatly pleased. Be warned that some folks hate tail-draggers and avoid them at all costs. I am the opposite. But then I always fly off grass and frequently with ruts and holes.
Damned ruts! This is my only current trike and it has a beefy Fults double nosewheel strut now.
Here's an old thread for you.
http://www.rcuniverse.com/forum/begi...l-dragger.html