Most likely (as stated above), the number of attaching bolts under the radiator support was different for different sized trucks in different years (making it hard to make general statements).
The 1947-55 Factory Assembly Manual (mostly showing 54/55 diagrams) shows the 3100 and 3600 models' radiator support to frame cross member attachment as having two bolts, and the 3800 and larger models had one bolt.
