Brake Bleeding Question, Weird Problem

[fierrogt]

Hey guys,
I have a '67 camaro that I just put Touring Classics C5-Hybrid front brakes and '00 Camaro rear discs. I have everything run and I gravity bled the system, then did the two-man method (Until I saw no bubbles in bleeder line). With the car off I have a firm pedal, as soon as the car starts in gets soft. The rear brakes can barely stop the wheels from turning on jack stands and pedal goes to the floor. Here are the things I have already done/checked:

-Bench-bled Master Cylinder
-Checked for Visual Leaks
-MC full of fluid
-Tapped calipers as I bled

I am not sure where to go from here. Could it be air trapped in the MC, and I need to bench bleed again? Thanks for the help



Forgot to add- It is a power booster setup and I am running the long pushrod.