If you are looking for an economical approach, the windage tray will help out a bunch. The gains however are not really in strength. The purpose of a main girdle is to keep the mains from walking (side to side movement) and attempt to evenly distribute the load seen as the cylinder fires, to the rest of the bottom end. This effectively makes the bottom of the motor more rigid and helps keep the crank turning properly without breaking. The real question here is what are you after? If you are looking to build big HP (read, over 400 at the crank) then a real main girdle should be a consideration for longevity and strength reasons. If you are simply looking to tie the bottom end together for a mildly modded approach, use the windage tray and enjoy the HP it frees up.
Paul
P.S. If you go the route of a girdle, carefully research the designs available. It is my understanding that the Morana unit requires machining a significant amount of material off the main caps which is something you certainly do not want to do.
