Static, welcome to the board! You should have started a new thread with your question - we buy blank threads by the gross, so they're cheap!
Changing the topic of a thread this way is bad form, called a thread hijack. But since this thread iis so old, I'll answer your question here anyway.
The purpose of the double-reservior master cylinder is to divide the brake system into two circuts - front and back. That way if the fluid leaks out of one, the other crcuit will still have stopping power. That's not very important in an off-road only vehicle, so I wouldn't bother upgrading.
But if you really want to do it, the best way is probably to take a complete system off of a junkyard truck, including at least the front axel. That way all of the components will work properly together. You can't put a MC from a disk-brake truck onto a front-drum system.
How much work the swap will require depends on the truck. Your Jeep has a closed-knuckle front axel, so it will probably have to be swapped out for the truck's front axel. You'll be switching to disk brakes, and no disk setup is going to bolt onto your Jeep's axel. It is probably possible to swap different drum brakes onto your front axel, but that would take a lot of work for very little gain.
I don't know what back axel your Jeep has, but you can probably switch brakes there as easily as re-drilling the mounting holes in the backing plate.