What are the specs for a sbc casting number 378999?

I don't believe 378999 is a valid casting number for a block or head, however, check the website,www.mortec.com, for SBC casting number information.

For Chevy cylinder head specs, try this one:

http://www.73-87.com/chevy_ids/sbheads.htm

And, another good site for block suffix codes, block casting numbers, and cylinder head specs:

http://www.chevy-camaro.com/chevy-camaro-engine-codes.asp

Thanks,

dave