Hi Brian,
I am going against the popular opinion here and saying to use the Enya 29. It is not a real bad vibrator, and has plenty of power to fly the Yak! I would just set it in a rich two stroke and let her go. A 10-4 to 10-5 prop depending on how fast you like to sport fly. I have mine set up for a Veco 19BB and hope to get it finished soon.
As to the LA 25, it would be a good one, also. The FP 20-25 engines are great, but you have two engines there that will work fine, already, for your purposes. Great thing about Enyas is that they are almost impossible to wear out unless they are really abused!
Mongo