BK,
I personaly have no experience with that feed pump but I do recall reading about machining them in a older (I think) Live Steam magazine. The author stated he had real problems getting them to work till he realised just how critical each dimension was for the internal parts and bores. I think he stated that all dimensions had to be held to .001 or less to get them to work as designed. Sorry I can't be of more help. Maybe someone else here can recall the artical I'm thinking of.
Pete