I have a 73 barracuda with a manual transmission and manual brakes, is there any difference in my pedal assembly than what they used in a power brake car

There is a bell crank that goes between the pedal and the booster.

OT from what I understand they both have the same brakeing force just that PB require less leg to apply that force & they do give less actual feel. Is there an issue with the manual brakes right now? we might be able to solve it.

If you cannot find original linkage parts, a kit like the attached would do it.

https://www.mpbrakes.com/images/MPB-F200-49.pdf

If you want chevy, and ford parts on your car.

FWIW, the dual diaphragm booster pictured is basically a re-pop of the Hemi booster. Smaller diameter (8" dual vs 9" single) is handy for clearance and the "dual" part gives more boost which is nice for harder hi-po pads... also smaller piston area aftermarket calipers.

I run a similar booster with OE 1970 "E" PB linkage and it works well. If I did not have the linkage already, I might buy a kit as pictured.

Brewers should have what you need.

http://www.brewersperformance.com/products.php?cat=279