RE: GP Decathlon 40
Did build one of those...Had an OS 46SF on it, with a J-tec inverted incowl muffler. Flew great. Careful with the CG, and do no spin if not a little nose heavy...took 2 1/2 turns to recover, Otherwise, great model. Landing gear a little weak, tailwheel is crap, better replace with spring leaf tailwheel bracket. Did use K&S Aluminium profile tube for struts, balsa provided was so hard, btut the plane flew great without struts, Also, my kit was from 92, so I do ot know what they changed since then, but the wheel axel was actualy screws, in orteher to attach wheelpants also, either you change the axels, or you put some brass tube on the thread where the wheel are gonna be placed. I did have some wheels that seized, locked, with some bad results.
Good luck
Al