while the early blocks are a little stronger, they both will handle 600HP. if you can get a set of the older 70-71 heads, they'll flow better than the later ones.. you can make some serious HP with a 460 for pretty cheap with 450-500HP and lots of torque..
the car wont handle as good, but it'll go...
BTW, I thought about a 347 for my 68 stang.. but decided on a 514 big block..
oh yeah, go here for tons of 460 tech
http://www.network54.com/Forum/85220