The bolts are 7/16 course thread,the length is dependent on the stand set up.I say any common bolt will work, grade 8 is just more money.I rebuilt 3 stovebolt engines using what ever bolts I found laying around. You're threading into cast iron which will break long before the bolt ever does.A 3/8 non graded threaded rod can support 500 lbs in shear or tension,the grade 2 bolts at the hardware store are generally forged with rolled threads,more than adequate, grade 5 will triple insurance.
