By fuel pump casing, do you mean the housing that holds the fuel pumps?
We have been rebuilding these units using new/refurbished fuel injection pumps. We haven't had much problem getting these assemblies as yet, but you are correct in that things are going to be damn hard too find in very short order. I work on tugs in the Canadian Arctic and I can tell you that there are alot of these Cats everywhere up here, oil rigs and shore instals. We have all been informed that parts might be getting harder to come by. Even the old EMD's, but luckily GE has taken over building the power packs. They now have a very updated version with an increase in compression and output power with lower emisions. We are going to have an interesting start this coming season, we have vessels wintering all over the Arctic. This Global warming trend sure as hell is not making itself known in the Canadian Arctic. This past winter has been the coldest on record. I hope my boat is still floating!!!