pedal to booster ratio mechanism

[weq92f]

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My 67 has been updated to power Disc/Drum using what appears to be a CPP upgrade kit. The only thing left of that system is the booster and its connection through the firewall to the pedal. I'm thinking of replacing this final component to help with my current brake issue: not enough brake force is being applied to the MC to lock up the wheels. I've replaced pads/rotors/calipers/MC already.

If I drive along for a few minutes, the first stomp on the brake pedal feels pretty good and does provide a LOT of brake force. However, if I let off the pedal and reapply pressure once or twice in quick succession, the pedal becomes low and stiff and does NOT provide enough clamping force to the calipers...If I use extraordinary force on the pedal at this moment, I can get more clamping.

The booster installed does not have any ratio modifying mechanism between it and the firewall...it's just a straight horizontal rod going all the way to the pedal. I've noticed both types of boosters available in the aftermarket...my question here is do I need this ratio modifying mechanism? It appears to be a lever between the pedal rod and the booster rod that increases the plunger push over what just the brake rod would deliver alone...

EDIT: pictures are for reference only.

Thanks,

-Kevin