73 Manual Disc/drum Master cyl no residual valve

So I did the 8.8 explorer rear w / discs swap a few months ago and I'm just to the point of driving it and have noticed that ( although stops ok ) seems biased to the rear. Feels like stopping a fwd car with the e brake a little.

Car is a 73 Duster that had manual disc/drum setup.
Here is the kicker...Neither the current master cyl OR the old one on the shelf have residual valves in the outlet for the rear brakes. I've even taken the old one apart to see if it's part of the plunger setup and it's not. There was no spring or plunger behind either seat

Am I losing it?

I'm not opposed to getting a new master cyl.

Just to be clear, all of the proportioning happens in the proportioning valve, correct? or is any of it done in the master cyl itself?

I suppose I'll just get an adjustable proportioning valve ( probably some new lines and master cyl as well ) , but I'm just really confused as to why the old MC's don't have the valves..