Need opinion from those that KNOW.

You have the original master cylinder, so which every way you proceed keep your old master.
Chrysler used one of their cost saving ideas relating to master cylinders. They had two housings, one with two equal size reservoirs and one with a large and small reservoir.
By the mid seventies all of the same size reservoirs were sold and they were replaced with the disc style master cylinder. So if you went to the dealership with the original style master, they sold you the disc type master as a replacement. It was cheaper for Chrysler to have different bore sizes while still using one housing. What's really confusing is they both had the same part number. Some of the aftermarket master cylinders did the same.
Looks like Raybestos still has the original style.
If you decide to rebuild, then this is the proper kit.
https://www.ebay.com/itm/3645553557...dymKNuhfHfCg4uArCyrjIDdvTn|tkp:Bk9SR-jR9eb7Yg