Done. Here is a review of my process as well.
I used 1/2" UHMW or some such high-impact plastic sheet, cut the shape from the middle and then cut the aluminum to cover the cavity. Both aluminum and the form were screwed down (all 4 corners) to a thick wood piece. My tool was a UHMW piece that I made on my mill, with a hole bored in back for the chisel tool to fit. The chisel was simply a pointed tool from Harbor Freight cut down flat at the end. I wasn't sure how it would hold up, but the larger tools held their shape perfectly, but the finer tool I made was slightly deformed at the end after making 3 panels.
The 3003 aluminum forms so easily and has a ton of stretch to it. It is also easily annealed so you can get even more stretch out of it. I was able to easily anneal with a propane torch, going enough until the flame bouncing off the specific area I was heating turned orange.
Once I had a technique, I was able to form a side in about 20-30 min, of course the rough shaping takes less than 10 but the finalizing of the shape to get everything nice and smooth is the time consuming part. Over the course of probably 4-5 hours, I was able to make the form, make 3 pieces for one side and the other side as well.
I already have a 1.5" cap and a sight glass coming, and the air/oil separator return is almost complete. I think the most challenging part will be forming the aluminum strip around the perimeter of the two end pieces and getting it nice and symmetrical, but not sure yet.
