As mentioned located the mains a  bit in front of the CG.  I wouldn't re-use the stock mains but rather look for a lightweight set of main gear something like this: http://www3.towerhobbies.com/cgi-bin...LXNM65&P=6     The fuselage looks to be made out of heavier balsa sheet so you may be alright with installing/gluing  a plywood block on the inside bottom . Use some blind nuts and blots to attach the mains.
For the tail wheel you could use something like this: http://www3.towerhobbies.com/cgi-bin...LXD850&P=7