Does anybody have the measurements for the round body/base of the head diameter of this model?

I do not have this unit, but may pick them up for the R4 astromech as I need a roughly 1/48 version to fit in a Banda 1/48 X-wing

The answer you seek is right here (measured from the bottom of the base, so take that into account)

I don't have the R4, but I measured the R5, as they appear to be identical apart from the head. The body is 11mm in diameter, not including the shoulders for the legs. With the leg-shoulders included, it's 15mm. Looking at the head of the R4, it looks a bit wider than the body, so maybe add another mm or two.

Hopefully you'll get some use out of this 🙂