Great work on the engine, Dan. Nice scratching.

As far as the bottom wing is concerned, I have had some success just butt joining if things are thin and light enough and my rigging functional but a couple of pins is probably better. I always have trouble getting things lined up properly so I also do something else...
I make the lower wings one piece and cut the shape out of the lower fuselage and attach it that way. There is some filling, but it's strong and no worries about lining up pins.
Just an alternative. Looking forward to more progress on this one!
Dan (P.S. I've got that "Aces High March" stuck in my head thanks to Larry over on HS! It could go equally well with your build

)