Small block or big block?? Small block are all the same size 2 1/16 x 3/8-16. Big block have 2 longer bolts and are also 3/8-16. I think ive seen them both suggested but since you need no more than 15/20lbs that grade 5 will work best.
Every SB LA factory cylinder head rocker shaft bolts are 5/16. Plenty of busted bolts out there because of messed up info in a service manual. IMO, look at the bolt, see what the diameter is and find a good reference for torque. Grade 5 and grade 8 bolts have different stretch properties, requiring different torque values.
