Brake master cylinder and booster

[jasonda]

I am currently building a 1968 k20 4x4. I am using mid 70s axles and brakes and will be upgrading the manual brakes to power. Before I buy a new master cylinder and brake booster I was wondering is there any difference or advantages to using a mid 70s master cylinder and booster verses the correct year? I know they make different bore master cylinders and was not sure if there are any differences in these years.