The problem with a '67 B-Body with disc brakes is that they all used the 'Hemi' offset booster regardless of what motor was installed. I am not sure just what you have there but you should have a bracket assembly between the booster and the firewall. If you do, have your booster rebuilt by someone like Power Brake Booster (https://boosterdeweyexchange.com/). I can't comment on alternatives as I only have worked with the stock setup. Here is a picture of what your bracket should look like if you have the stock assembly.