With stock heads you won't be able to use stud mount rockers unless they heads have been machined for them. The stock heads are set up for pedestal mount rockers. Stock ratio is 1.6 if I am not mistaken. I have a set of 1.6 scorpion pedestal mount(bolt down) roller rockers. Lots of guys also use the Crane bolt down 1.7s
The bolt used for pedestal mount rockers is a 5/16" bolt
There are 1.6:1 , 1.7:1 and 1.72:1 ratios and it all depends on the cam you have. Stock heads don't flow much after .550 lift, hell they don't flow much peroid. But, first look at what cam, duration, lift and then decide what rockers will suite your needs. Make sure they are pedestal like RYC CUKR said.
Copy this then paste it in the address bar. You need to be looking at the pedestal mount rockers. Unless you have had machine work to mount stud rockers. I would recomend part number 778-66879.
Hope it helps.