A hidden VIN code separates GM’s last true first-generation small block from any other 350, and most owners never learn where to look for it. The Vortec 5700 L31 quietly powered Escalades, Suburbans, and full-size trucks through the late 1990s, while its oversized cousin, the 400 cubic inch small block, carried its own quirks and a notorious overheating flaw. Read on to find out what separates these two small blocks from the rest of the Chevy family, and why one of them is still available brand new today.