440 in 73 Dart Sport, Convert to Manual Brakes?

The master cylinder is different for manual and power brakes.
Do yourself a favor and buy a new one from Dr.Diff with the proper push rod and offset mount and you will never look back.
Call him and he'll set you up with what you need.
Mopar Aluminum Master Cylinder Kit
Or, u can save a few $ by buying an offset mounting block off ebay, and lengthening the existing pushrod the same thickness as the new offset block, and get an 87 dodge diplomat /alum. master cyl. from an auto parts store. I did, it has a pedal feel about twice of power brakes.