RE: Need help selecting the proper size engine
Adam,
.074's would do nothing for this size plane. 15's would be the absolute minimum if you built light enough. I flew a Royal b-17 with OS .25 BB engines and it was a great combination and the 17 is a 78" span.
Remember if you are underpowered there is nothing you can do but get bigger engines but, if you are overpowered you have a throttle to slow her down.
Todd