Modification to a 4 drum master cylinder for use on 4 wheel discsv. ?

A disc drum master will still be wrong for your application. Yes you can remove a residual check valve in the rear circuit of a disc drum master but the reservoir is still too small for your rear disc brakes.

buy the attached link below master cylinder and you’ll be golden.

Mopar Aluminum Master Cylinder Kit

rear disc brakes aren’t era correct either. And disc drum master will have too small of a reservoir to support disc brakes. Not enough volume..

safety is more important than trying to keep your master looking correct, especially if the rust right away and look like crap like most do.