Anyone know if ARP makes an undercut rocker stud for a big block, and what the part number is? I have some new rockers with thicker shafts and want to be sure I'm getting enough oil to the Rockers.

T&D has them. I think ARP makes them for T&D but I don't think you can buy them directly from ARP.

Measure and mark the stud for the location of the center of the rocker shaft. Place stud in a drill, and then grind or file them undersize (because I don't have a lathe.)

Put one of the new studs into the bolt holes on the shafts and look at them
If you think the oil doesn't have enough room to flow around them then deal with it then
All the H.D. after market rocker shafts I've seen and used had a hoop of clearance around all the bolt holes, a bunch to big 1/4 to 3/8 inch end to end total movement on the bolts or studs with no pushrods installed

You did not say the brand, but the standard diameter sized rocker shaft should not have a problem. The T&D rockers uses a smaller than stock diameter shaft that is pretty thick to where the stud blocks oil flow. T&D supplies the kit with under cut studs.
Because I did away with the stock rocker stands and used billet aluminum Max Wedge type rocker stand "blocks", I needed longer hold down studs that still needed to be under cut (except the bolts at the ends of the shafts.)

Thanks guys,these are Mancini rockers made by Harland,so stock diameter shafts here.The shafts are considerably thicker than the cranes I am replacing which is why it got me to thinking about turned down studs,but from what some of you are saying,I may be overthinking it here,and the regular stud will be fine. I may in the future try to turn down these studs a little bit, or call T&D, but for now I'm crunched with time trying to make a race this Saturday,and will go beat on it the way it is!