Distribution block change?!

Working on a '70 Duster. Was a 4wheel drum car, converting to disc brakes. I got the front disc brake kit from CPP. It's all installed.

Now I'm down to the master cylinder and distribution block. I figured I'd just use a mid '70s disc brake master cylinder.

My real concern is the distribution block. Can I just leave the factory block in place and add a proportioning valve to the rear line, or does the factory block have a proportioning aspect to it? Would it need to be removed or changed, or can I leave it?

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