Is there difference between MC for power vs manual?

gdizzle said
So is it possible that the M80266, that states for Rear Discs, does that mean I am missing the residual valve I should have since my rear is still drums??? I thought the M80266 was on the interchange list, but ???

Who knows. By the time stuff gets entered into the web its been copied a half dozen times, and nobody checks whether its right or even makes sense.
Now just think about this. Chrysler never offered rear disk brakes on these cars. Any M/C listed for original application for those years ('67-'74) should have a residual valve in the front outlet (rear brake feed). Earlier years had the residual valve in the distribution block, and later years used an 'expander' in the rear cylinders.
You can see the residual valve in good light. 1970 Chrysler Imperial Hydraulic Brake Service Guide from the Master Technicians Service Conference Session 274

gdizzle said
Also I have installed an adj proportioning valve to the rear, and I have it wide open and it still does not lock up.

Did the fronts lock up? If the answer is no, then your test wasn't close to the situation prop valve needs to be adjusted for. Follow the guidance on the instruction sheet and set it close to the factory setting. Factory setting was to initiate pressure control above 300 psi. Same booklet as linked above explains that.
Then once you get everything working correctly, if you want to further tune it, take the car out to the slickest situation you can safely test in. Adjust it so the rears don't lock up first under hard panic braking.