2000 Camaro Brake Booster - HELP!

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I finished installing C4 front calipers and 2000 Camaro booster and master cylinder (after modifying the booster) on my 69 GTO and the booster doesn’t seem to work??



It fells the same with the engine running or not. I do have the vacuum hooked up and I have a new check valve.
I have no assist…the car does stop but it’s like I have manual brakes.

Could the booster be bad? How can you tell?

Is there another booster that will bolt up and work with the MC I have?
I do not want to modify another booster; really just want to finish and drive.

Thanks