I agree, you are on the right track I also have a Futaba 6exa that works fine for me although I wish it had a mix for dual elevator servos.
The OS 46FX would be a good choice but I would stay away from the Evolution engines there are only a few people at our club with these some have ran well other did not. OS engines are expensive so if you want to save a few dollars on the engine I would recomend Super Tigre other people have had luck with some of the "OS clones" made by Magnum or Tower but I have never used them. No matter what brand of engine you choose pick stay in the .46-.50 range because it is a more versitle size and will have more uses in future aircraft than the .40.