Another Disc Brake Installation Question

[NoNeck]

I am installing a new Wilwood Master Cylinder onto a new CPP Brake Booster. The instructions that came with the Brake Booster were for installing a CPP Proportioning Valve. Just my luck... and I couldn't find anything to help on the CPP website.

The photos attached show three Master Cylinder pushrods. The top one labeled "A" is the one removed from my old Delco Remy booster. "B" and "C" are pushrods that were included with the Wilwood Master Cylinder. I believe I will need to use the longer pushrod "B", but does the O-Ring install through the hole of the booster? Also, what is the smaller pin and which direction does it fit?

The large rubber/steel washer on pushrod "A" inserted into the booster and remained on the outside. It looks like it is encapsulated inside the CPP booster.

Any help or photos would be greatly appreciated. Thanks!