There are two stud sizes I am aware of, 3/8 which is what most stock pressed in studs are and 7/16 which are found in higher performance engines and are generally of the screw in type. You can retrofit heads from 3/8 to 7/16. There is no performance gain associated with the stud size that I can determine. The rocker ratio determines how long the valves stay open and care has to be taken to ensure an increase in the ratio does not cause a valve to contact the piston. I do not claim to be an expert on this so I would suggest doing a google search for more detailed information. Unless you are building your small block to a high compression configuration the 1:52 rockers would be more than adequate for your needs. I am using them inconjuction with an Edelbrock performer cam in my 350.

This style of roller rocker does not need periodic adjustment. There are some others which may if used in a mechanical lifter valve train. The hydraulic lifters do not require this adjustment once they are set correctly.