Master cylinder sizing

[66fury]

I need some input about master cylinder sizing. I had installed an ssbc disc conversion on my 66 plymouth. I have the master still on car that came with kit but size is unknown, but is late 60's master for disc /drum car.i changed spindles to a later year to take advantage of bigger stock rotors and add first gen viper/brembo calipers . I was wanting to change out my master to a wilwood unit and not sure which would be best.what do i need to know in order to choose the right one.