Ok,
My car was changed to the dual reservoir brake system using the 67 setup. Its manual drum brakes

Issue is I have a brake fluid leak I cant get to stop. leaks form under the cap. ( ive changed cap and gasket , and it still leaks a little.

I have decided to just buy a new master cylinder.
Question is,
I have been thinking about converting to disc brakes at some point in the near future and am wondering if I just buy a disc brake master now, is it compatible with my drum brakes till I actually convert it to disc brakes

OR if I buy a drum brake master cylinder can I retain it when / if I convert to disc brakes. Im looking at one of these new master cylinders at the moment
I am thinking conversion will not happen for a year or so ( I have other fish to fry before making that swap )