Well I finally found the info I was looking for.
I'm posting it here in case it's useful to anyone else.
There are two numbers but it's all for the same kit.
<<These are the actual part numbers,
Delco #PT391 and GM #12102762.
I ordered a new plug w/pigtails from a Chevy Dealer.
Just came in Friday, It's the exact plug I needed.
Spliced it in with the supplied connectors and it runs fine!>>
For some reason without these part numbers if you go to a Chevy Dealer they claim you have to buy the entire harness and can't seem to find the kit == even if you tell them it exists.