Allen:
4 to 5 pounds / .82 four stroke! Are you sure you need that much engine? I have put .90 four strokes in scale ships before, but they were in the 13 pound range. Once off the ground, they flew at about 1/3 throttle (or less). I am just wondering if that size engine won't become the largest part of the weight of the model. In the last couple of decades it seems like we have transitioned (both in R/C and CL) to HUGE motors. I guess what I am trying to say is if you are trying to keep the model weight down, won't that large an engine defeat that purpose? Now, when you build the full-bodied copy, with that large round cowl and considerable more weight, I'll bet that .82 would be a perfect application.
Jim Fruit