I have '35, '36 and '37 NG's (one part restored, two in bits..). Unfortunately, I don't have the correct mudguard for the 1936, but my '37 has an original front guard similar to the one in the photo. My '34 LH also has narrower 20" rims. I think they all did pre war. I've never seen an LG, but I think they do too (so, not a 250). I think the one in the photo is a 19" and being painted, this points to a "G" model.
I think only the 500 Hunter had a quick action throttle in the mid 30's, not the 350 NH. As you say, the gap under the tank does suggest a 350.
Looking at the better photo, I'm pretty sure about the knee pads, so I will put my money on a 1936 NG / De-Luxe.
I hope you can find more info and a current owner!
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.