I have built several Black Hawk Musciano hollow log kits and a scratched a couple hollow logs from Scientific plans.  Several of the plans show cowls but there is no details about them. How were the cowls made?    Were they spun or formed metal, aluminum, formed plastic, or some sheet metal the builder fashioned into something that looks lit the box top picture?  Any info or pics would be greatly appreciated. Thanks

I would guess a hardwood buck is fashioned, and then thin aluminum is beat around the form.
I had to do this for a hand-formed motorcycle fairing piece. In that instance, I used a piece of hand-sanded and shaped maple. The 1/16" aluminum sheet was screwed along one side of the buck, and soft woods used to "hammer" the aluminum sheet down and around the buck.
The last bit of shaping was with a 1/2" pice of plywood with a hole cut to fit around the base of the buck. This was placed over the aluminum, and beat down around the edge to pull the aluminum closer to the buck, creating a light crease and flange at the base of the panel.
Harder and faster to describe than do, but the work turned out fine.