Your springs will dictate what you need as far as valve length goes. Keep in mind that long valves/tall stands make for problems with valve cover clearance.
I'm using T&D rockers and they specify the 5.140 valves. They sell rocker stand spacers that allow fine tuning the rocker stands to get the rocker tip sweep correct.
I've talked to them a couple times and they have been very helpful even to a schmoe like me.
