EPOXY some 1/4" plywood inside the fuselage so that the landing gear axles will be even with the leading edge of the wing when the gear is in place. I suggest adding some triangle stock to re-enforce the ply gear plate.

Glue a piece of 1/8" - 3/16" ply in the tail to fasten a tailwheel to. I prefer the Sullivan tailwheel setups for ease of installation.

Rebalance the plane - the CG stays the same.