I don't like to tell people what to do, especially when a manufacturer is supplying a system.
What I can say is that most factory disk brake systems have a larger resevoir for the caliper pistons. Unlike a drum brake's wheel cylinder, as the pad linings wear the caliper pistons use signifcantly more fluid to backfill the space.
I used a converted drum brake master for a at least a decade with no issues. Just explaining why the factroy added a larger resevoir. Up until '67, Chrysler stacked additional resevoir capacity on top of the standard master.
My point was not to toss the master cylinder you have. Even if it needs bore sleeve it may be worth something.
"Mastershake" on Moparts wrote an article on correct master cylinder castings and part numbers, back when he worked for big brake company. He's made some updates and corrections since it originally came out but still a good starting point. I *think* the pdf version has the corrections.
Moparts - Members In Print, Brad Schroeder "Pumping Points", Mopar Action (jpgs)
http://www.moparts.org/Tech/MoparAction/Master_Cylinder.pdf
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Thanks... I always like getting feedback so don't hold back. It's data points for decisions.
I agree in what you mention about reservoir size and disc/drum combinations. I'll go with the "system" package and see what happens I suppose. Figure I'll give it a chance to be correct
What's interesting is that the old one was with the car having drums all the way around....