Tophe: as far as I know, enlistment means just that. Able-bodied men were drafted or enlisted. Enlisting meant some choice of Branch (such as Air Corps) then basic training, specialist school, staging, and deployment. Someone recognized as a designer for a strategic industry like aviation would receive an exemption or deferment from service.
Sunny belt: much of the USAAC/USAAF training Army was done in that 'Sun Belt' to take advantage of the flying weather (same rationale for much of the BCATP being in the Canadian Prairies).
The Air Corps had already moved its Tactical School from Langley to Maxwell Field for that exact reason. Maxwell Field was als0 home to an Officer Candidate School and much preflight training (sometimes by civilian instructors) which later included combat glider training.
Duhamel design: the nose reminded me of the Uhu as well

For powerplant, I was thinking of one of the so-called Hyper engines such as the horizontally-opposed 12-cylinder Lycoming O-1230 or Continental IV-1430/XI-1430.
AFAIK, the only 'joined' Ranger was the V-770, a V-12 but too small for a fighter like Dehamel's. Menasco worked on Hyper engines but those were (unbuilt) inverted Vs or H engines (XIV-2020 and XH-4070).