What size are the cyl head studs in a 170?

I was finishing up the cooling system repairs on my 65 Valiant that has a 170 slant six in it and I got to the point of adding the coolant and of course it shot right out of the head. I thought I cracked a block in the hard freeze we've been having. But I looked at where it was coming from and noticed there was a stud missing and water was coming right out. I thought they didn't start the cooling jackets on the manifold studs until 73? So does anyone know what size/length the studs are, so I can just get one and seal it and install it back?
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