The best advice I have for anyone building the kit is go electric. The weight shift that occurs in flight while the fuel is drained makes the plane nose heavy. Keep in mind that the plane is balanced out with a full tank of fuel and you'll need to add a lot of nose weight if you don't use electric. With electric, you won't have that problem. An e-Flite .46 outrunner will work. Also install that servos in the wing for the ailerons and rudders with direct drive and not with the cables included with the kit. Keep in mind that if you add a retractable nose gear that when you retract it, it will shift the weigh back quite a bit. If you can find a set of fiberglass wheel pants use then instead of building them as instructed in the kit.
This build for the Sig Tristar will help. I have built one and still have it & it builds very similar to the St. Croix version.
http://www.rcuniverse.com/forum/m_52..._1/key_/tm.htm
Saul