Maybe one of the Ryan military trainers? PT or ST? Looks a little like the Ryan PT-16, but not exactly.
That's really what's driving me nuts, here...it looks like a LOT of planes, but not exactly.
There are probably about five major design features that, together, make this a fairly unusual aircraft. One can often find two or three on a candidate, but I haven't yet found a candidate with four.
These are:
1. Radial Engine
2. Low-wing open-cockpit design with all-metal construction.
3. Horizontal stabilizer mounted atop the aft fuselage (vs. mid-mounting)
4. Fuselage-mounted landing gear
5. Unusual taper of the lower fuselage forward of the wing
#2 is probably the loosest...after all, it could be an early production aircraft with open cockpits, while most were built with canopies, or a subsequent owner may have metalized the wings.
But it's #4 and especially #5 that eliminate most airplanes. I haven't yet found that strange taper...most of the candidates mentioned (Ryan PT-22, Fairchild PT-23) are round like a barrel, here. The O-47 is somewhat tapered, but it has a mid-wing, not a low wing.
Nor have I yet found a candidate with fuselage-mounted gear... the Ryan, the Fairchild, and the North American all have wing-mounted gear.
The gear is a puzzlement. It obviously can't move, so either it's got bungees or something near the axles, or it's totally rigid like a Fly Baby...and what works on an A65 powered single-seater is probably NOT going to handle a big, all-metal, radial-powered monster. Could this be a temporary structure, in lieu of the normal wing-mounted gear? But there's easier ways to do that than to run tubing deep within the fuselage, and the spar butts don't look hefty enough to handle landing loads.
This one's a toughie.
Ron Wanttaja