Tips for replacing intake manifold/headers

I have almost everything I need to start my 4 barrel and header conversion. I started looking over the studs and hardware on my 225's head. I do not feel comfortable with keeping the old studs and risking snapping them when I torque the bolts, my header instructions indicate 26 ft lbs of torque. I have never removed studs on a slant 6 head before. Therefore besides hitting them with PB blaster for 3 days in a row, what other things should I consider?

If I put 2 nuts on each stud will that work for getting them out?

Also I have 2 new expansion nuts for the end bolts, what should I use for the rest, grade 8 nuts?

I also need to buy grade 8 threaded studs, I am not sure what size and thread pitch they are. I wanted to buy these before starting.