"U53", Denotes that being a 1953 Chevrolet COE 5700 series. If it has a inside the cab fuel tank, it's definitely not a '48 model. '47, & '48 model G.M. COE's had frame mounted fuel tanks.

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