Could someone help us?  We are trying to check whether the engine in our 78 Corvette is the original or a crated one.  The engine number matches. Also, could someone please tell us what the casting number GM3970010 K12 and the engine number, 1Z8748S41 mean.  How can we tell if it is a 2 bolt or 4 bolt main? Any help will be greatly appreciated.

Welcome to C3VR!

The 3970010 block was used for several years of production, and would be correct for a 350 in '78. It is usually a 2 bolt main engine, however, if this is an L-82(and yours is), it could possibly be a 4 bolt. No way to tell without actually looking.

1Z8748S41=
1Z= Chevrolet
87= Coupe
4= L-82 ("L" would be a base L-48)
8= 1978
S= St. Louis assy plant
1= This is a "check" digit...really means nothing to anyone except law enforcement, or REALLY serious restorers. IT is part of a mathematical sequence.

This alpha-numeric sequence is your VIN. The last 6 numbers(which you did not list) is the sequential build number of the car...meaning the number of the car in the build. Example: 400001 would be the first car built of that year model. The last 6 numbers will start with a number that really doesn't apply to the actual number of cars built, as far as Corvette assembly goes, since they never made that many(6 digit figure) in any one year of production. The first number is basically a place holder, and is usually a "4".
hth

and congratulations on getting a vette.

and sorry about the crap that follows, i've got some kind of bug....

(bug exterminated)
Adams' Apple2011-06-12 17:19:22