In all seriousness.. Go with the Genesis, just not the first batch IF and WHEN they come out. This has been going on since April of 2000, when a Genesis iron block was priced at $1700 and the aluminum was $2000.. The original ship date was suppose to be April 15, (should have been April 1.. April fools day) They haven't and won't be for a good long time.. Go to their website..
http://www.genesis427.com/
The notion you will find a Shelby 427 block for 6k is not likely.. Shelby documented 427's have risen dramatically and if you can find one it will be generally sold as a complete engine (or scrap) and will go for well over 13-15k.. (I know because I bought one)
There are NOS service blocks being sold for 5k.. Those will need extensive
oil passage porting, they should be decked and line bored to insure correct geometry.. In short you are probably going to have 6k in a service block.
A better choice might be a seasoned (late model) std. bore to .015-.020 over bore. As the bore goes up the price goes down.. Later engines (late '66+) had thicker, squared cylinder walls.. As well as provisions for hydraulic lifters..
Stay away from the coasts.. If you can buy an engine in the south or mid west you will be better off.. They seem to have tons of old stuff laying around from various 60's racing efforts, NASCAR and NHRA..
Ebay will often have 427's available.. BEWARE.. a good number of these are warmed over low HP marine engines, 1/2 of which were reverse rotation units and while look like side oilers are not..
If I had it to do over and I didn't want to spend big money on an FE I might go buy a 385 series crate motor (429-460) which now can be had in 502 rated at 500+ hp
Good Luck,