rocker shaft studs

Does anyone know the dimensions of rocker shaft studs? I'm going to have a local shop make me a set of grade 8 ones.I'm using 273 adjustables with stock hold downs and my push rods are about .020 too long.I figured studs would make the shims easier to install.I know I should just get shorter ones but am planning to do a 408 over next winter and hate to spend the money on rods for 1 season.I need to know overall length and length of threads on either end.I know the threads on the block side are 5/16ths,should I go with fine threads on the shaft side?