CONFUSED! Small Block Casting #'s

I just obtained a chevy small block that I was told was a 350. I pulled this information off the block:
Casting: #3858174
Casting Date: A276
Engine Code: FOI29YW
No Partial VIN on block
"Clock" casting symbol
Based on the casting # I understand this should have originally been a 64-67 327 from a fullsize Chevelle, a Corvette, Camaro, or truck. The hp should range anyway between 275-350. The "clock" symbol was suppossedly put on blocks made mainly in Saginaw. The casting date says the engine was assembled on Jan 27, 1966. NOW, here's the confusing part. Based on the engine code suffix...YW...this should be a 427 BIG BLOCK. I have not mistaken the numbers...they are very visible and clear.
If anyone has any idea what might be going on PLEASE let me know!
Thanks

http://www.chevyasylum.com/tech/decode.html

Code YW is listed in my book as a 1966 327 cubic inch 185 horsepower L32 engine with a manual transmission and a 2bbl carb.
It was installed in a 60 series truck.

mike in tucson

It has a automatic transmission if that helps.

Sorry, but the MSA-1 book only lists the manual transmission 60 series truck for this letter code for a small block. You should pull the pan and see if it is a small journal crank.....cranks and flexplates get changed over the years.

mike in tucson

So do transmisions:HMMM: auto/ stick its a 327 two bolt main 64-67

Additional Info:

3858174 - 327ci produced 1964 to 1967, 2 bolt block
F0129YW

F = Flint Plant
01 = January
29 = 29th day of January
YW = 1966 truck, 185hp, 2 barrel carb w/manual transmission

That's not to say this engine could not have been swapped into something else - however, it came from the factory in a 1966 truck with a manual transmission.

If it were a big block, you are correct in stating that it would be a 427, 216hp, 4 barrel carb w/manual transmission (C60 series truck)

and it was born 43+ years ago.....it has probably been apart a couple of times.

This block could be considered a mystery block. Chevrolet documentation shows the block being used as early as the 1964 model year in 300 plus application and commercial trucks. Verifiable proof of this model usage was not found until 1966. This block was used interchangeably with the #3858180 block in some applications. Passenger 327-275HP 2-bolt, Chevelle 327-275 &350HP 2-bolt in March 1966 introduction, and Chevelle 327-300 & 327-350 2-bolts.