Drum Brake Wheel Cylinders 2881613 casting vs 2881612?

[robl72]

Looking to understand what the difference in casting numbers was for rear drum brake wheels cylinders 2881613 vs 2881612. I have a 69 Charger R/T, Nov 68 build.

Any idea which number is more correct for my application or are they both?

Thank you!

 

[gtx6970]

size of the bore?
Size of the bolts holding it in place ?

 

[robl72]

size of the bore?
Size of the bolts holding it in place ?

Thanks for the response. Bolts are the larger 7/16 -20. Not sure on the bore size but a standard replacement is listed as .9375 ". Do you know which one is correct for my 11" HD Drums. I have a manual brake 11", four drum system on my stock 69 charger 440 R/T Auto Trans, 8 3/4 Suregrip.