Smallest/Closest mounting power steering pump?

You would end up with something from a more modern Jeep, anything else modern.
I know Volvo's have nice little steering pumps where the pulley itself is larger than the pump housing. But the pulley will need to be changed to a V-belt anyway.

You need to be aware of the pressure output of the modern steering pumps. They are mostly higher than the old ones and could damage the steering box seals.

Enter "power steering pump" in Google Images and see how cute and tiny the modern steering pumps are these days.