You may want to take a look at J.E. Howell Model Engine Plans Home Page Jerry did number of plans for Hot Air and Internal combustion engines from entry level to advanced. Hit and miss to V four and a few other things. Worth a look
For what it's worth I have the 12X24 Grizzly and I'm very satisfied with it. Check out the specs. I drove from Rhode Island to get mine. Spent the night and drove back the next day.