I'm going to throw out a few bits of info (grains of salt) until there is someone with a GMC shop manual and factory assembly manual to verify and do a better job at helping. Are all the parts from a 1946 GMC truck? The big trucks, ton and above, may have a wider yoke and maybe different mounts.
Chevrolet AD trucks have spacers underneath the radiator yoke but 1" sounds like too much distance to me. There could be vibration pads on the GMC that the AD trucks does not have. Unfortunately (for the aggravation) the whole front clip, including the hood, is assembled but not tightened. Move the clip to get good hood alignment with the cowl at middle and both sides to get the gaps correct then snug all the bolts. If before the de-installation of the hood hinges, they were located with witness marks and/or drilled location holes, you have something to go by. If not, I would look to the shop manual procedure for hinge installation.