Steve I used the same elbows for my V-twin also the Simplex and the Harley Peashooter. I'm convinced many of the early engine builders used the same plumbing in various sizes. Right off the hardware shelves. Why cast your own?
The motor is coming along great. The head fins are running in opposition, I favor the rear cylinders look, Though fins on the front cylinder would cool better. You don't require cooling. On the originals the rear cylinder was the one designers worried about running hot.
The tubes look rad & at the same time proper. Pipes ran all over the place on originals, typical of a make therefore covers a lot of ground that restorers agonize over but we don't have to. Typical for the type is more appropriate, with much latitude in execution. So I like what you've done!
Rick C.