I doubt the measurement box is capable of using operators with the push/pull tool.

I would use the measurement tool to mark out the full dimension you're after, then use that as a guide to push/pull the surface to.

So for example if you got your extrusion at 167mm length and you want it 400mm long. Select the measurement tool, click at one corner of the extrusion, then move the mouse in the direction you want to go in and enter 400 in the measurement box. That gives you a reference to take the push/pull operation to. No complex maths involved, lol, just a few extra clicks.