So I have a 70's frame with a 400cid in it, still dont know anymore if this is even a chevelle or truck, these numbers have pointed in both directions, I hope someone can help me figure this out.
front passenger pad shows 14J121821 T0921CTA
Rear drivers side by bell housing reads GM
3951509

In my searching Ive found the engine was from the Tonawanda plant in NY, sept 21...but the CTA sometimes adds the lt4 application, which throws me off also...it had a 2brrl carb on the engine as well...

Any help would be so grateful....trying to find out what i have and what its from

 

This might help you if you haven't already seen it.

https://nastyz28.com/sbchevy/sblock.html

 

Yes that's where part of my info came from, but in digging deeper it seems the CTA denotation sometimes points to a code U LT4 and the best i can find off that is a chevelle, but then that in turns tries to tell me its a 4 barrel carb, but its a 2..so i dont even know if this was a 400 from a c10/c20 or some version of a chevelle, then on some lists, hte 3591509 can be listed twice, indicating a 2 OR 4 bolt main, but most things i see only list this code as a 2 bolt.