Not sure that these pictures are enough to tell if it's a 235 or 261. Looks like Captains bars over the starter. Can't see if there are bars under the manifolds. Casting numbers were covered with grunge and stuff. Looks like external oil line loop which would be on a 261. The truck is pre 54 but the motor could have been changed.
http://1drv.ms/N5tvhG The wrecker is a 48....working on a deal. The yellow Chey, maybe a 2 ton 55? Couldn't get to it. 1965? 4x4 nobody home. Yes, I'm going back!