Power brake conversion question

[Misstur_big]

I converted to power frt. disc and drum rear on my 67. I started out with a factory style booster but I dident like the look or feel. I purchased a aftermarket unit 9" booster with a vette style master cylinder. It also has one of those self adjusting prop valves.
The pedal feels a little hard too me. It is the same feeling I had with the factory unit. I do have a check valve installed for the booster so thats not the problem. I am running a Gen 3 engine 5.7.
Do you think I am just not generating enough vaccum with this motor?
I dont have any problems stopping. It just feels like there's not enough travel in the pedal.
I just wondering if anyone else has made this conversion with a Gen 3 engine is experiancing the same issue.
Thanks for the feedback