What do I need and what do I don’t!

Might be seeing an interlock override on the left fender
Photo here. If so, scroll down to Townsend's post in the same thread for a way to rewire.

EGR and Cat speed switch are shown in this one. Any idea what this is?

Engine connector shown here 6. Cylinder duster is now a 340 ignition issues wants to start when you let up on the key
It was a convenience for engine install but is also a vulnerbility.