Ok ... it looks like the SSBC calipers have 2 - 45mm pistons for a total area of 4.92 sq.". The mid-70's Mopar calipers have 1 - 2.75" piston for a total area of 5.93 sq."

Given that most of the manual brake upgrades using those Mopar calipers use the 1-1/32" m/c bore the caliper bore to m/c bore ratio is 14.3:1.

In your case, using the 1-1/8 bore m/c, your ratio is 9.94:1.

In other words, its taking almost 50% MORE effort to apply your brakes.

To get close to the 14:1 ratio you'd have to go to a m/c with a bore of 15/16".

NOTE: all of the above calculations are for comparison only and DO NOT take the rear wheel cylinder volumes into account.