I searched the Cummins Quickserve Website and found that 3936318 and 3936316 are two different pumps, and that they are part numbers at the end
of a long supercession of part numbers. Technical bulletin 00T5-16 describes
the latest versions (3936318, 3936316, and others) as being modified versions of the Federal Mogul supplied pumps that have been changed by FM to reduce noise (as if we could hear the darn things anyway). If you want to
supply your engine serial number, I can confirm your list pump part number for you, and determine if there are newer part numbers that you can use.
As for the physical differences between the two pumps, I cannot tell from the website. That's not how the site works. But... . if Cummins has bothered to keep multiple part numbers for 12 valve lift pumps, there is a reason.....
Steven