The fender braces on the 1937 BA97 are shown in the catalog cut above as flat but it's hard to see in my picture. I looked past the down tube because of the sweetheart sprocket and the rear fender braces which are on the OP's bike. The serial number is basically useless, BUT it fits 1937 in one of the pre war serial number tables. Below, see the straight down tube, but also see the wrong sprocket and fender in the picture of the 1936 B97.OP bike has a straight down tube and not curved like the catalog pic shown here. 37 fender braces were tubular and not flat. Who knows what was swapped out but with what’s on the bike now would lead me to believe it’s a 36 B model. Also very common for fully dressed B model motorbikes to have 4 leaf clover skip tooth chain rings.