Master Cylinder Install question

I'm getting ready to change out the single bowl master cylinder for a dual bowl on my '31 Ford that is mounted on the frame rail. I have drum brakes all the way around and was wondering if I needed residual valves in the lines. The current single bowl doesn't have them but a lot of things the previous owner had done didn't make sense so I don't want that to be my guide. Thanks

maybe the single bowl has a residual valve built in?

I would say yes, add valves.

To expand; if the master cylinder is mounted lower than the wheel cylinders then residual check valves are used to eliminate the possibility of fluid "draining back" to the master reservoir.