[RichardJ]

>>Also, the first and last bolts are just alignment dowels. But a lot of guys thread them out and put bolts in to better fasten the manifold.<<

For a stock cast iron manifold, most agree to leave the pins alone so the manifold is free to expand as Chevy designed it. If you use aftermarket tube headers then you should remove the pins and replace with threaded studs. In fact, it is better to replace all the manifold bolts with threaded studs. There are already two threaded studs to start with.