RE: 4 stroke exhaust header
I took the elbow that comes with the engine and cut it in two and purchased a 3/8 copper 90 degree el and silver soldered the two pieces of manifold into each end, screwed them together and had a 90 degree manifold. this was for a 91 so you might need to adjust the sizes to suit.This was for an inverted installion with exhaust coming out the bottom of the cowle the same as you are doing I think.