56 Ford F-250 Power Assist Brakes

I am building a 56 Ford F-250 long box into a flatbed with duallies. I have dual wheels front and back (front required arrow head adaptors). I want to upgrade to power assist steering but probably going to keep drum brakes front and rear becasue of the dual wheels.

If I use the power steering assist that replaces the stock master cylinder under the drivers side floor, will the stock access to fill the brake fluid resivoir still work to add and check brake fluid?

How much increase in performace would I see from this upgrade using stock drum brake shoes front and back?

Is this simply a matter of replacing the stock brake resivoir?