Magnum 318 questions.

Both front and both rear intake manifold bolts usually corrode badly. Sometimes they break during removal. I usually replace those bolts with a new set from Felpro, or at the very least get four from the junk yard, but remove them from center positions on the donor engine.
I think they are said to be torque-to-yield anyway. It works fine with grade five hardware if those are cheaper.
When you put it back together, keep cylinders number five and seven spark plug wires away from each other in the looms to prevent crossfiring.