The 20cc gassers have been used in many .60 size birds with much success and there is no reason it should not work just fine in your P-47. I am currently flying two 64 inch span Hellcats with 20cc gassers and while they are more power than needed they are certainly not too much. Scale models of radial engine warbird types almost always need nose weight to balance anyway so the use of the larger and heavier gassers does not necessarily lead to an increase in the finished weight. My .02 cents.