Wheel cylinder mounting bolts

[GTX]

I just replaced a rear wheel cylinder and noticed that the mounting bolt holes were smaller diameter than the one I took off. I guess it makes little difference as long as you have the correct bolts.
Am I missing something? Did I get the wrong one or were there different sizes? Where would I get the correct bolts? Mopar parts counter??  Is maybe the cylinder for a smaller drivetrain app? It's supposed to be for a 383 car. Maybe the cylinder is supposed to be a little larger bore and also have larger bolts?

Oh, app is '68 Charger right rear 10" brakes.

[histoy]

I ran into a similar problem when I was looking for rear wheel cylinders for a '70 Plymouth.  The factory wheel cylinders had 5/16" bolts and all the replacements I found had 1/4" bolts.  I ended up drilling the 1/4" bolt holes in the wheel cylinders to a larger size and tapped the holes to accept the 5/16" bolt size.

[68 RT]

Home Depot, Lowes, any automotive store.