Manual brakes never used a bellcrank. The pedal is linked directly to the master on every muscle-era and later Mopar with manual brakes that I've ever seen. Try to add a bellcrank and the pushrod won't align to the master cylinder, which is critical since the pushrod has to be locked into it with a rubber bushing on a manual-brake application.
Changing the size of the lines will accomplish absolutely nothing, as 68 said. The only changes lie in the sizes of the bores of the master, caliper, and wheel cylinders.
If I were guessing, I'd say your "manual brake" master cylinder is not as advertised, or at least not correct. Manual brakes often use a larger bore on the piston than power brakes to move more fluid for the same pedal travel. I'm thinking you've got one with a 15/16" bore, where you should have one with a 1-1/32" bore. It's very possible your parts guy got you the wrong one. You could also try swapping down to a smaller bore in the wheel cylinders, but I've never had to do that on a manual-brake swap. It will also affect your proportioning as they will actuate more quickly. Which brings us to...
The metering block. It's also possible that you got the wrong unit there. Even if you have the right one, the proportioning is rarely good much less optimal. I much prefer to run the front brakes directly off the master via a tee, and do the same with the rear brakes using an adjustable proportioning valve such as a Wilwood or Allstar. That's what's happening with my Valiant, and it's quite likely I'll do the same on the Challenger, Imperial and the wagon as well.
