Alot of factors, but knowing the year really helps.
In '46 the 2 ton trucks usually have a vac booster for the brakes on the opposite side of the frame from master cylinder, the 1.5 tons usually dont. The presence of that vac booster and the longer wheel base is a good indicator of weither it's a 1.5 or a 2 ton, but it's still nothing more than a "probably is".
In newer Chevy vehicles (like in the 50's) the series number was put out on the hood, and you can tell quick what it is based on the series number.
If you can provide us with year, make, model (if known) and a picture, i'm sure between all of us we can figure it out.
