changing a head gasket 350 engine

Can i get at this head (one side only) by unduing just one side of the intake manifold or do i have to remove the entire intake manifold? Anything else i need to know or do before i start on this? 1991 gmc sierra

Pull the intake manifold. It's the classic head gasket job. Doesn't get any easier than this. Just be sure you have some reference material to follow and review the valve adjustment proceedure closely. Valve adjustment and distributor installation are about the only things people screw up!

Is there a link on this site that i am not finding, with proper instructions on head gasket replacement? I need to have the engine on TDC before i start , correct?

Google is your friend! No it doesn't need to be on TDC to change the head. But it will have to be to adjust the valves and setting the distributor.