I built two of these planes from Rich Uravitch and they had a 50 inch span. Rich called for a .60 four stroke but I use OS .46s in both. These were very heavy little planes the way they were drawn but the .46 pulled them quite well. As fly stated, a .70 four stroke would probably work out very well in the size you are wanting to build. The full scale had a water cooled V-8 as I recall so it the model didn't come out as tail heavy as a round engine Bipe but it still needed some lead up front. The four stroke may be the answer to that little problem. Have fun with the build, they are pretty straight forward planes.