Master cylinder - brake pushrod

Folks, I have a kit for front disc conversion picked up through Mancini.. car is a 67 dart. Keeping drum rear / installing disc front (or getting a shop to do it rather) but, my master was leeking and pealing the paint off the firewall so I went ahead and pulled it to at least get that taken care of then the new mancini part MRE 3360.
Mancini racing Dual Inline Master Cylinder

Pulled the original master and had to remove the brake push rod from the pedal to pull out in one unit. I then pulled the brake pushrod connected to the rubber seal internals out of the MC.. Ok now I am stuck.. the brake push rod is connected somehow inside the seals & spring mechanism. There is a phillips on the end of the spring cap.. anyway, I need to replace the master so..
1) The Mancini part is a 3 hole MC, mine is 4 and no adapter.. most likely returning as I don't want to deal with drilling / conversion.
2) is this even the right MC MRE 3360 part to use for my Dart conversion.. maybe a mute points per above point #1.
3) I am at a loss with separating the brake pushrod from the other piece (name??)
4) if I do separate the brake rod from the spring by removing that Philips screw (which is stuck) Then, will the break rod work with an aftermarket MC?
5) There are plenty of threads to source the right either Chrysler or Dorman part so I am good there.. unless you would like to throw in your advise on the best MC for the job.

photos of the rod and orig. mc attached

so obviously new, learning, but at a loss.

MC brake rod.jpg

MC.jpg