i have used two starter bolts they are 3/8 16 NC they can be grade 5 . any hardware should have them .it s is hard to get a to torque wrenche in there .' but i have a built in torque in my arm ' ha ha
i use threadlocker loctite on them crank to fly wheel 65. and conveter ??? uses threadlocker and say 45 to 50 this should give you a ideal on the torque.