I have done that with several planes, the only difference is a slightly slower snap rate. Didn't affect the plane's looks much, nobody noticed. I moved a Saito 180 3 inches forward on a Cap 232 when I pulled the gas engine out, the weight and balance issue was the same as yours. Do it. You can build spacers to fill any gaps, and a lot of the old Classics had air behind the engine. Where I lucked out was the Cap had a long engine cowl, I could put the engine anywhere I wanted.