I recently removed an SBC from an 87 Monte SS that the previous owner claimed to be a 305. Afterpressure washing, the stamping number read 5.7 LG SG1. The pass. rear casting number reads 14093638 which also comes out to be a 350. I contacted the previous owner who said the owner before him said that is the original engine as far as he knows. The 87 Montes only came out with 305s. If I'm correct the 305 has the same stroke but a smaller bore than the 350, right? Is it possible that the block is a 350 core but still a 305 bore? I really hate to tear into it just yet to confirm. The other funny thing is that all the block plugs are brass and the timing cover and oil pan bolts are kinda clean for a 130K motor which leads me to believe someones been in here before. Any input guys? Thanks

 

Nope, you have a 350, 1987-95 vintage...period...exclamation point! I wouldn't complain, nor would I bother to open it up either. And no, GM wouldn't have built a 305 using a 350 block. Besides, the blocks weren't cast with that much extra cylinder wall thickness. And one of the previous owners said it's the original engine "as far as he knows"? Just how far back does he know the history of the car anyway?