Since the distance from it’s base to the point on the ground where the hook would land is fixed, the “leverage” placed on the base can not change.

Raising and lowering a given load, in the position shown, should be no problem; other than you can not place it into anything (like a pickup truck bed).

But as you “boom-down” the load (i.e. to place it in a pickup truck bed) the leverage increases; the closer the load is to the horizontal the greater the amount of counter-weight needed; in effect, the load increases.

The “lever-age” is created by the distance from the base of the mast, and the point on the ground where the hook would land. Obviously as the boom lowers, the distance to the hook (lever) increases.

Unworkable at best, dangerous at worst. Sorry.

Crane in an Urn
Crane in a bottle

PortaLift

The problem i see:
1) the box sized payload would be too close to the boom
2) Cranes are difficult to use in office environments, and who really knows rigging? Or has the right chokers and slings?
3) The legs need to be spread further for better anti-weeble-wobble/topple.
4) What is your power source?

Other thoughts:
Will this have load shutdown features like real cranes?
You might consider tensionarity for your machine.

FWIW Something like this (very durable) already exists in the construction world:
Sumner Manufacturing ROUST-A-BOUT
They also make duct lifts that look like manual forklifts, something better for boxes.