I have a drum drum mc same as yours in a non power factory disc brake 67 barracuda with zero issues. I also have a disc brake mc that you're looking for if interested.
Yes I would be interested.
Is it just old, or reman?
Regardless of some opinions, the service manual and MOPAR specs note that the larger reservoir is needed for front disc brakes.
That would be the explanation for concerning "travel", despite a 4 piston upgrade.