Pressure in the oil pan a noted problem with older Cats. We used to check the oil with the old Cat with the engine running. Anyway if you rebuild the upper end, head, valves, injectors. If your not using any oil and while your doing that, change the main bearings, front and rears seals and you should be good till a million mile mark. I don't know your engine but I would not change to another engine manufacturer without changing trucks, it's just to costly and can be something that will give you heartburn for a long time. I might ad that this process can be done w/out pulling the engine and with the right machine shop you should not be down more than about 5 days. If a shop is doing it than it depends on the shop. I would sure get estimates before letting someone else do it.