In my opinion, it's a 1951 model. Only year for pull down door handles, & door vent glass. '47-'50 models have a driver side cowl vent. 1952 450, or 470 would have a 302 in it. You just need to figure out if it's a 450, or 470 series.

Spanky Hardy
Collector Of Fine Old G.M. COE Trucks & Antique Holmes Wreckers

1948 Chevrolet 5700 COE Holmes HD W35 Wrecker
In the Stovebolt Gallery
More pictures on Photobucket

1950 GMC 250 1-Ton
In the Stovebolt Gallery