I have a 1970 Chevelle Malibu. It had a 400 big block engine, which some jerk took out. I'm in the process of finding a 400 to rebuild. I found an engine and the owner states its a 1973 400 SMALL block. The Malibu 400's were discontinued in 1972 but were they still making 400 BIG blocks, or is the engine a small block? The casting # is 390817.

The listing is here http://boston.craigslist.org/nwb/pts/403665666.html
What I guess I really want to know is this guy correct in calling this engine a small block, or does he not know what hes talking about? Did they ever make a 400 that was a small block?

yes they did, lots of them and that block is one of them per the casting number. That's the block I have in mt car right now. It's essentially a bored and stroked 350, just done at the factory.

The BB 400 is just slightly overbored 396. If you can find a 396 block you're sitting pretty. Easiest deal to do? build a 454, it looks identical from the outside. Very few people can tell the difference without detailed inspection. With a 454 block and a 396 crank you have a 427, which have always been good running engines.