My friend has an 87 Z28 that i'm doing a cam swap for him. The engine was replaced (or so the seller says) with a 350 and it only had about 16k miles on it. Well I was going to check the suffix codes but the middle one is gone and cannot be read. What I can read is U-A but that tells me its a 350 or 305. Which doesn't help. So while doing the swap I check the codes on the back only to see that their different from any other motor i'v checked. The codes on the back are GM S./LG and SG1 i'm not sure what these mean, but their not normal codes. I think he said he got the motor from Advance Auto or something, I would assume they rebuild old Chevy cores though and it should have normal stamping codes. Anyone know what these numbers and letter mean? Any help is greatly appreciated.

 

Actually, I just checked the other side and found the right numbers! How weird that the numbers are switched around? I thought all chevy engines had the numbers in the same place? Is this not true?

 

The common locations for block casting numbers and I.D. numbers are as follows:

 

No, they're always in the same place....

Look at the casting number. The stamping code might have got obliterated in the rebuild process. Vader's pic shows clearly where to look. That number absolutely does not lie, it tells you at least with complete certainty what the bore is (which is the dimension that's different between a 305 and 350).