I too have a 37 GMC, it is a T16 and it has the bumper with the dip in it. I assume it to be original. I bought the truck from the original owners grandson when I was 14 almost 30 years ago. Mine had a 216 in it when I got it. It has been off the road for too long, hope to get back to it soon.

Jason

1937 GMC T16 468 BBC th350, 4.10
1941 Dodge COE 5.9 cummins, 9 speed roadranger
1947 Diamond T COE, hercules and 4 spd, all original
1955 Chevy LCF 9.0L IH diesel AT545
1962 Corvair (Elsie)
1967 Jeepster Commando
1968 K10
1970 Chevy C50 box truck