Not the braking I want

Well, the OP made the change hoping for better,but was he experiencing this problem before, or did the swap create &/or
exacerbate the problem? FYI,mopar used 3.10" piston calipers
on all disc brake combos,8.25 thru dana60 w/duo servo 12X3"
rear drums.Using 11.75" or 12.82" rotors as the change up frt.
If your new MC has a larger bore/piston for the frt discs,you've
lost braking power,I've seen that happen before. It looks as tho'
you have the proper metering valve at the frt. lines(under the
rubber cap),but it's impossible to tell what pressure it's set at.
Mopars OE cut-in was 117psi, if yours is too high,you will get a
higher amt. of rear apply B4 the frts. start working. The valve in
the rear may be the residual check valve,which holds 5-10lbs. of
pressure against the wheel cyl. seals to keep them from drawing
in moisture/air when they cool down. Some MC's have this in-
corporated in them however. Lastly, you could see if you can get
a smaller wheel cyl. dia. than what you have now to balance things.