@Bextreme04 @Ricko1966 I did some late after work snooping, and found at least one issue that is resolved. I had wrongly assumed that the dark green wire that was for the temp sensor was the right one- I need to check if it's on the same circuit via the diagram- but the "electric choke" wire was actually the temperature sensor wire. I peeled back the loom, way back and found that it was also dark green. Grounded it, gauge to hot, no blown fuses. Hooked that wire up to a spare temp sensor since I'd purchased one at one point thinking that was the problem, and since it was cold, I hooked the wire up to that and grounded the temp sensor....gauge back to cold.
So the next task is to find the light blue wire on the diagram that is supposed to be for the choke, it comes off the oil pressure sensor. I don't see it looking back there, but it could be hidden, or maybe it wasn't kept when swapping from the straight six to the SBC. After reading up on why GM did it that way, makes sense that the electric choke doesn't get power until it gets oil pressure, but maybe I'm wrong about that.
That'll be for tomorrow after I'm rested. Off to watch Vice Grip Garage, then hitting the sack.