This info is mostly wrong, where did you get it?

D0HP is either a casting or ID engineering number prefix, on what part did you find it? Following the prefix, is a 4 or 5 digit basic number (begins with 7), followed by a 1 or 2 digit suffix.

Casting numbers are foundry marks, cannot be cross referenced to Ford part numbers, but ID engineering numbers can be crossed over to part numbers.

H has nothing to do with Holman-Moody, it's just the 3rd digit of the casting number prefix that FoMoCo used on some parts, and...

There was no such thing as Motorcraft prior to 1973!

In 1972, the US Gov't forced FoMoCo to sell Auto-Lite, as they claimed FoMoCo had a monopoly on auto parts.

In 1973, FoMoCo introduced in-house brand Motorcraft, all the former Auto-Lite part numbers became Motorcraft part numbers.

 

Best to look closer at those digits. The 3rd digit of
"H" has always referenced Heavy Trucks. Like a L9000 Louisville. And there were no C4s in heavy trucks.