Engine search

[LuckyRabbit4]

I've posted a few times about this truck but this one should be fairly easy for someone who works with these trucks often.

I have a 66 c10 and I blew the head gasket. I've been working to get the whole engine rebuilt but decided to stick with a new gasket kit and deal with suspension/brakes/steering.

What I found out is that the engine isn't original at all. Casting number is 377127, vin is F1004CCF. That's from a 1976 car with a TH200 Auto transmission. My truck again is a 1966 3 speed on the tree.

My question is, what transmission came stock on these trucks, assuming it was an inline 6 the whole time. May of had a v8 in it stock and was swapped out, I'm not sure. Trying to decode the VIN number to see what engine could have been in it to start.

Need to know what the transmission could possibly be. And if anyone knows more about what vehicle the engine itself came out of.