Looks like an L-model or an early R-model with the double rear windows.
It could have a Red Diamond 6-cyl. engine. Displacements from 372-501 cubic inches were available. These, for the most part, were solid performing engines. Thirsty, but dependable.
These trucks were well built. You could take an arc welder to the sheet metal if you wanted to.
My dad has a early '60's R-190. It was a tandem tractor that was stretched and had a 20' dump bed put on it. It has a RD-450 and an 8-speed Road-Ranger in it. I don't know how tight the turning radius was before stretching it, but turning a tight corner with it isn't possible now. Driving that truck gives you a lot of respect for truckers 50+ years ago.