on 67 chevelles with drum brakes is there a difference between power brake master cylinders and manual brake master cylinders? If so what is the difference? Thanks in advance.

No difference.
When I converted to power (drum) brakes, all I did was bolt a PB booster between the original master cylinder and the firewall. Didn't even have to loosen the brake lines, just repositioned them. Just use the previously unused hole (there are two) in the brake pedal frame for the new booster pushrod.
Works great!

The reason I ask is after I replaced my master cylinder, during the brake bleeding process the pedal would only go half way to the floor,( no fluid pressure yet) so I unbolted the master from the booster and the pedal now pushes to the floor. I am thinking that maybe they have a different stroke? Am I wrong in thinking that the pedal should hit the floor prior to building fluid pressure? As it is now the pedal only has about 3 inches of travel, just doesn't seem right.

Something is not right. Better figure it out before a road test. Did you bench bleed first? Maybe the m/c is bottoming from hydro lock. Does the pedal drop if you break the lines at the m/c loose?

Yes the master was bench bleed, I have reinstalled it with lines disconnected and no fluid in it to check the travel. Now it has full travel at the pedal. As Denny stated above, maybe the m/c is bottoming from hydro lock. I would say it is. I never run into this before. How does it happen and what do I do to fix this problem?