Orion,

The exhaust elbow is a relatively complex geometry that also fits into a fairly tight space.  While I am sure replicating it from measurements and sketches alone could be done, the chances of getting something wrong would be pretty high.  Here is a picture of one for reference:  https://amelyachtowners.groups.io/g/main/photo/84403/13?p=Name,,onan,20,1,0,0  

--
Mark McGovern
SM #440 Cara
Deale, MD USA