Tony wrote:
....
... Ask Dad if it's a 1/2 ton truck. If so
legally you can carry a total of 1000#, ...

There is no state that I'm aware of that has load tag limits on
light-duty trucks other than the highway axle limits that are far beyond
what OP's asking to carry so legality is not going to an issue whatsoever.

The overall vehicle weight rating is the limiting limit but there's a
lot of conservatism in them compared to reality.

The possible actual limiting factor for an old truck w/ almost no miles
_MIGHT_ be the condition of the tires--are they still original or have
they been replaced sometime in a relatively recent time frame?

The actual GVWR for the actual vehicle will be on a plate on the door
column or in the glove box or somewhere else on the vehicle. If it's
this pristine, there's likely the OEM book in the glove box as well.

As for the half-, 3/4-ton, etc., it is as someone noted, only a class
rating that distinguishes basic group of
axles/suspension/transmission/engine packages available. Each
manufacturer is a little different but each tries to out-spec the other
by a few pounds in their ratings for advertising purposes so they can
tout "highest payload" and so they leapfrog each other from one model
year to another.

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