Adjustable Proportioning Valve - Required for Disc/Drum Setup??

[Rack Man]

I'm plumbing the brake lines for my 70 K-10 project....I swapped the front axle to a mid 70's Dana 44 w/Disc Brakes (rears are still drum).....I ordered all new SS lines from Inline tube (which 50% are too short)....They also sent me an adjustable proportioning valve...Is this valve necessary even with the regular proportioning valve located at the master cylinder?....or is it meant for fine tuning the rear drums in more of a performance application?

Thanks in advance for any insight you can give me!

Dan