Studs to bolt stock exhaust to aluminum heads
The holes in the manifolds are bigger for expansion so the studs do not shear from expansion and contraction. a special conical washer is used on the end studs only. The rest of the bolts do not get any. so you will need 4. make sure you use a exhaust stud. a carb stud will shear.
Cummin's diesels have very large spacers for the same reason. I have repaired many that have sheared. They sell two piece manifolds for them do to shrinkage from excess heat.
So this said don't try to perfect a design that is there for a reason. they will shear. Unless your afraid of the power and never get-em red.
5/16 studs 13/32 holes is the way they were designed. Use the conical washers.
Your welcome Steve