Not a unique problem. If memory serves me right, they changed the headlight styles sometime in 1937. My truck came with the smaller lights that did not have the recess for mounting (can on right). I have bought and restored one bucket and discovered that it was the later style (can on left). I ended up getting another one to match the smaller size and that's what I used.
I did confirm with Alan that his 1937 used the larger style cans with the depressed area for mounting. The smaller ones were also used on autos, but the way. Personally, I would be comfortable with either style, but if you want to err on the side of what is correct, you can use the larger ones. Hope this is of some help.
Vic