Re: 1965 GMC Truck Ignition Switch
 

The truck was purchased without switch or ignition key or nut. Just the harness I pictured in the attachments.

Re: 1965 GMC Truck Ignition Switch
 

Can not find a separate switch that fits your connector. This may be something that will work.
This page has your connector configuration and the switch and tumbler info. The connector fits their switch even though the switch is missing an unused terminal. I have looked for someone else in the past. This whole Chevy/GMC/Car/Truck ignition switch thing is all screwed up by the vendors. 4, 5, 6 and 7 contact switches out there. If you need a new connector like yours, they are available, but all the aftermarket switches don't fit that connector. The vendors don't sell a connector with their switch. Only AAW has a switch and connector (which is not original as they explain). It's the only thing I could find.

I still say the best option is that switch I linked, and you purchased. Wire it up with female spade terminals. Every vendor sell that one as a replacement. Always will be available.

Maybe a used donor or NOS would be your thing.