There are kits available for your 38 master cylinder. If the pits won't hone out there are people that sleeve them with brass or stainless. Only two things influence how your master cylinder performs; the bore size in it versus the wheel cylinder bore size and the ratio of the brake lever itself. Your original MC will work fine with the brakes it was designed to actuate or with newer ones if the wheel cylinder bore size is the same size as the 38. If the wheel cylinder bore size is more than an 1/8" larger on the newer brakes then you will not have enough pedal stroke or if it's smaller there will be full pedal but it will be very hard and take too much pedal pressure. Unless one runs over some road debris or tears open the system in some other way then brake failure is 99% the fault of the owner. Inspection of the steel and rubber lines, noting and correcting any leak, and immediately investigating when the brakes feel different will make brake failure non existent. Having boosters and disc brakes on a vehicle with 600-16 bias ply tires is kind of like using a sledge hammer to drive in carpet tacks. If you go to a big engine and sticky tires then all of that is a necessity but not for a 38 that is still the way it left the factory with gearing that limits speed to about 50 mph.
