Starter wiring

[C15_Sierra]

Maybe I'm overthinking this and there's a really simple answer...but here it is

Truck is a 1980 GMC, swap engine is a 5.3L from a '00 Silverado, right now I'm using the stock underhood fuse block from the Silverado to power my engine harness

I've gone as far as I can on my own to figure out what I need to connect to the cab in order to get everything turning. Online diagrams aren't helping (even tho they should, maybe I'm just an electrical idiot? ). I've identified some of the wires on the engine side of the firewall that go into the cab, but not all of them. I'd post pics if they would help, but its such a clusterf**k that it'll probably better serve to confuse than to help.

-What wires do I need to connect to the battery/ignition switch/charging circuit?
-Is there a specific/separate input that goes into the fuse block for the starter solenoid?

I'll probably have more questions as I knock out the final wiring stages, so please bear with me...you guys rulel