poor brakes on 71 K20

[Murphy IRE]

OK I've looked through as many threads as I can. There is a lot of good advice and a lot of stuff I need to check. Here is the deal - The pedal is stiff (1/2" free travel, the lights come on at 3/4" & total travel is less than 3"), but I can't get the wheels to lock up on dirt. I do have boost (I will measure to see how much). I stopped the truck with the engine off and it was really tough to stop, so I know I'm getting boost!
Here is what I've done so far:
Replaced the front rotors, calipers, pads and up graded to SS flex lines
Replaced the rear drums, shoes, wheel cylinders and up graded to SS flex lines.
The PO said he replaced the booster with a Delco.
I'm attaching pics of the MC. The brake lines are two different sizes. The large should go to the rear and the smaller to the front. BUT which reservoir should the lines come from? Are they backwards?
A lot of the previous threads have solved the problem with a new MC so that will be my next purchase, but I want the lines to be correct.
Also, the prices on MC range from $18 (local parts store) to $70. Is there a real differnce? As always thanks in advance