The Stovebolt Site Forums The Shop Area Engine Shop get dual master cly. Where?Rear ratio?

I'm going to use my ol'40 half tonne to carry a dirt bike and pull a ATV trailer in the Idaho backremotes. Where can I get a dual master cylinder??? Thanks Tonnes. Jim pea ess, with a rebuit 261 in the Chev, and using it in tough country, should I install my 3:55 or leave the 4:10 rear end alone ? Thanks again.