I've tried to get some basic dimensions, but was told they were "SSS". I have since "swagged" some dimensions, using fotos, and doing image ratio math, and am making some patterns. I have to decide on what to do for the flange side.
I may create some CAD drwgs, and have some pieces cut, and see what I end up with. {Probably, a lot of scrap}!
Downside is extensive welding time. I have MIG, TIG, and a spot welding machine, shrinker/stretcher, etc.. That's kinda like a 14 sec driver in a 10 sec car..
Downside to sheetmetal is wt. Alum not much better, & not as easy to weld.
Would be good to find a source for a custom vac molded product. I know of none.