Replacing single bowl master cylinder question

I am getting ready to change my master cylinder to a double bowl instead of a single. I have drums all the way around. Will I need a proportioning valve, or can I take the rear line off my block and go right to the master cylinder, then plug the block where the rear brake line was then the fronts would to the other bowl of the master cylinder?
I didn't think I would need one with drums all the way around just not sure.
Thanks in advance,
Paul