Power Disc Brakes Proportioning Valve

My 1970 dodge dart swingers proportioning valve started leaking and my brake pedal almost went to the floor! I took it to an auto repair shop and they say the proportioning valve I have on their now is incorrect. They are ordering a proportioning valve and new brake lines and say the cost will be $800! They want to redo the brake lines and put in a new proportioning valve.

Can anyone give me a link for the proper proportioning valve for a power front disc and rear drum 1970 dodge dart swinger? Classic Industries part:

http://www.classicindustries.com/product/mopar/a-body-dart-1963-76/parts/md2268.html

Is this correct? I would like to keep my brake lines.

Thank you!