Engine Number Mystery

So in my quest to learn more about my engine, I tried looking up the numbers. Some of the site that are linked from posts created some serious confusion. So I was hoping that someone could help me out with my numbers so I can figure out what I'm working with. Here we go:

Cast(raised) numbers on passenger side under the lifter plates: 328575 (under that)GM 71
Intake Manifold Cast numbers: 348303 GM 87
Engine code stamping below the distributor: F0211CJC and 13L173907

Any help would be appreciated.

Looks like you have a 250!

https://vintage-vans.forumotion.com/t4505-gm-l6-enginne-block-casting-numbers

Dan

Thanks Dan! I was told, by the previous owner, my engine was a 230. Any ideas on the stamped numbers? I looked up some numbers sites and found some confusing info. The engine was made in Flint on Feb 11. Part of the stamped number is "CJC" which they said corresponds to a Firebird. Is this possible or am I reading the charts wrong.

http://www.nastyz28.com/gm-chevy-codes/chevy-engine-codes-suffix-2.php

I don't doubt now that the engine isn't original, I just want to know what I have to be able to get the right parts.