010 350ci code not found

[Jesus5150]

So I've searched and searched but I'm not entirely how to phrase my search so what's seeming impossible to find may just be a syntax error, but I picked up a 350 today. It's a 39700010. I was told it's "a 4 bolt main 350 out of a Van". Ok, everyone has a 4 bolt main 350 until you look for yourself, so my hopes aren't high and besides I'm not going to build it so I don't really car what size or configuration it is.

My issue is when I run the date codes, they don't show up on any site. They are as follows;

C54106298 K11 II TWH

Now, TWH (Specifically the "H") Doesn't show up on the lists. But neither do Vans specifically, the only glimmer of hope I've found was searching for K11 itself which resulted in an RPO code stating "FLEET SALES SCHWANNS GO#V0144" which kinda sounds right, but an RPO code wouldn't be on an engine if I'm understanding correctly.

Ultimately it doesn't matter and this is all academic, but I WANT to understand how and why.

Can anyone illuminate this, or help me understand what these numbers are indicating so I can go search properly?

Many thanks.