Rocker arm shaft bolt size

5/16 grade 5 is ~13 ft/lbs. Still over 3300 lbs clamping force per bolt. Remember when you torque a bolt, you are stretching it slightly in its recoverable "elastic" zone. Anything more than 13 (for instance) would stretch it beyond its elastic zone where it could not recover and would just permanently stretch and weaken the bolt. Thats why good rod bolts have a dimple on the end so you can chuck up a bolt stretch gauge and use that instead of ft/lbs to get the proper "stretch". 'Snugging' a bolt just somewhat ensures it wont back itself off during normal use, and may be good enough on some apps but every bolt on a motor has a designed torque value that is followed when it is assembled and can be looked up. Some are crazy low like carb studs, barely only enough torque to prevent them from vibrating off, and slant 6 manifold bolts that are designed to let the clamping force allow some sliding of the manifolds themselves