Slymo, In theory the pump faces (body and drive spindle casting) should all be flat and in the same plane. The time honoured way was to assemble the pump, tightening the bolts bit by bit and twisting the body and spindle casing , checking all the time to try and stop it binding. Then rubbing the pump flat on a sheet of fine emery paper, supported on a piece of window glass. Then came the washing out of the emery dust and aluminium filings with petrol, turps or paraffin, whatever you had. These days blocking the holes would be a good idea....that was then.
An A65 pump gasket, with a strip cut out to shorten it, can be used to ensure all three pump mounting points are in the same plane in an attempt to stop the pump twisting as it is tightened against the crankcase.
Swarfy.