Remove the side bolt and get a longer one so you can lock the shaft position. With some pre-load on the indicator, rotate the shaft CCW. If the indicator reading immediately moves when you begin rotating the shaft, keep rotating CCW until it stops and zero the gauge.If the indicator reading did not change when you began rotating CCW then zero the gauge.Rotate CW until you get to the desired indicator reading. Lock the shaft with the side bolt.Place the hub on the shaft with the lock pin in place.Tighten the hub nut.Replace the side bolt with the proper bolt.
rover 300 pump has no bolt like that anywhere on the pump body. I looked, and looked, and looked again. Not there.