Why do you want something other than the stock unit?

There is a bracket available to convert to a dual master, and lots of possible masters that can be used with that bracket.

But on an otherwise stock system why do you want to change the master?

1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble...