They supply RCR (Nascar cup and Nationwide series) with their pushrods.
I'm slightly OR compared to stock, but not quite as much as INTENSE. I'm in between both (which is what you'll need because you don't turn the higher rpm'* like the S2 does).
Surprisingly, Dale Earnhardt died at Daytona with these in his motor.
You want 5/16x8"
They're one-piece chromoly.
Here'* a pic of the cross-section of an OEM:
This is a 3/32 (or .097" hole), my Smith Bro'* are .083:
I ordered these over the phone, they made them, engraved them, and had them at my door within 48 hours for less than OEM pushrods (GM price).