I have a 66 Chevy stepside and I'm wondering what is the engine. I don't think it's original.

Here's the relevant numbers found on the engine block (all are on passenger side)

B157 (I'm guessing this means Feb 15, and that last number could be 1967, 1977, 1987???)
877127 (I'm guessing this is the casting number,
and there's some possibility the first number is a 3 instead of an 8, so maybe it's 377127)

Stamped is the number F0217 CCF
I'm guessing this is Flint, Feb 17

CCF when run through the nastyz28 web page yields three engines:

1970 230 L6 140 GHP
1976 250 L6 105 NHP
1977 250 L6 110 NHP


So should I conclude that because of the "7" in the other number, that this is a 1977 250 engine?
Does the casting number help?

Just want to be sure I'm on the right track. Any other info you guys can provide would be much appreciated.

thanks,
Jeff
amato@nmsu.edu