Sounds like a cool project.

Btw, my understanding is that the P-38, done scale (ie, with out altering the dimentions, enlarging bits here and there and such) is a real monster in the air, and pretty much a gonner on engine out. There are a lot of other twins that handle engine-out a lot better than the P-38.

Back to your prop question, it's going to be a trial-and-error thing. 3 bladed props are actually less efficient than 2 bladed. The main (but not only) reason for using 3- and 4- bladed props is ground clearance or in other situations where a longer 2-bladed prop isn't possible.