You're right, C6DF-12127-H is not in the 72 MPC cross reference. C5DZ-(12127)-F is listed as a replacement for C5DF-12127-K, but is itself replaced by C4OZ-12127-F. The date code of 7H26, August 26, 1967 gives a clue of an early 68 application. The MPC I'm using lists Ford products, its absence might indicate a Mercury or light truck unit.
It's not the part number, but the components that make a difference, springs, weights, vacuum, etc. If you can have whoever is rebuilding yours put this one on a Sun Distributor machine (or equal) and read the curve, that might give you a better level of confidence.
Jim