RE: qm-15
hey there..
YES definately. Lots of folks have built the older QM15 aircraft with everythnig from OS25 power on up. The Jett 30 size engines will fit fine, and the performance will be outstanding!
You will have to accomodate the muffler slightly - should not be a big deal - should fit like a typical QM40 aircraft. Most folks never used the engine side cheek cowl anyway on the QM15 planes.
Firewall may have to move aft and grow in size slightly.
Most of the QM15 planes had a 1.5" spinner - Jett spinner will be a perfect fit.
Its a great combination - definately worth trying.