Thanks Graham, that's what I thought.
Dave, I wasn't aware of the old IPMS-C sheet, thanks for the tip and I will see if I can find out more about it and if it contained a second a/c. The origanal photo shows a long line of a/c (13) parked. Since my question was regarding the underwing markings, and only the nearest a/c showed these, I cropped the rest out for my question. You are correct, the Dak in the photo does have a diamond with "MP" on the nose. The next Dakota in line behind "MP" clearly shows "MF" in the same diamond and the code letter "F" is very clearly seen on the fuselage side underneath the port engine nacelle of "P". Unfortunately, the serial of this Dakota is not shown. Although they can't be read, it is apparent that the diamonds of the first 4 Dakotas all contain different second letters.