master cylinder replacement

[jroth100]

I have 77 k10 with stock power brakes and need to replace the master cylinder. Is there a difference between master cylinders used for 3/4 and 1 ton compared to 1/2. Is one better to use then another. thanks

[1976Scottsdale]

I know that the visual design is different on the two.  The 1/2 tons use a single cover retaining rod, the 3/4/1 tons use a dual retaining rod setup.  not sure on the rest.