I am interested in building up a 406 small block. What is the 406 based off of? Is it just a bored 400? Does anyone have any suggestions as far as what companies to go with to get a short block, either assembled or unassembled? Thanks.

there isn't really a 406, it's a 400 +.030. for a short block i'd look at GMPP see what they have.

Best thing to do if you want a 400, is to go the junkyard and get a core; then if you want something better than the stock rotating assembly, there are alot of affordable cranks and rods and pistons you can get. Look at Lunati and Eagle for some choices.