Some of the 60x engines have afterglow relays (you’ll find contrary opinions, they’re wrong.) Afterglow requires a different plug, regular plugs would burn out more quickly. My feeling is that anyone attempting to replace plugs in a 60x without pulling the manifold is a bit daft. And pulling the manifold gives you an opportunity to clean out the gunk, which will be epic if it hasn’t been done before.

Is u you our AC functional? AC, idle control, tach, transmission lockdown, EGR, and antilock all interact. Think twice about messing with them.