I framed up a Sig 71" Cub per the plans with original intentions to power it with a OS 40 2-stroke. I now have a OS 48 4-stroke which I want to install. Problem is, that the 4-stroke is about an inch to inch & a half longer than the 2-stroke (Due to the carb being on the rear of the engine) and in order to keep the overall length of the plane consistent with the plans I either need to (1) move the firewall back to compensate or (2) move the cowling forward with the 4-stroker. Moving the firewall back will require considerably more work, but I am afraid that if I do not the plane will be very nose heavy and will not look scale with the extended nose. What would you do? Thanks for your opinions.