Build the 360. Aftermarket engine parts are easier to find and cheaper, more piston choices etc. You're rebuilding it, so you can set the compression up the way you want it anyway. The biggest drawback to the 360 is the cast crank and external balance, but you'd have to get an earlier 340 to get the forged crank anyway. And if you're planning on staying under 500 hp you won't need a forged crank to begin with.Good deals on 340's are getting hard to come by.
A modern rebuild and some fairly moderate upgrades can get the 360 over 400 hp with no reliability issues at all. Check out this page for dyno results from a bunch of 360's, should give you an idea of the kind of HP you can make with some minor upgrades. http://www.mopar1.us/dyno.html
Realistically I think the 360 is just as good of an engine as the 340. The 340 might rev a little faster, but on that note the 360 should have slightly better torque all things being equal. The 340 just has more historical significance, but if you don't have a 340 car to begin with the 360 is the way to go, they're easier and cheaper to find and build.
Its kinda like a 6-pack setup. It sounds and looks cool because of the history behind it, but in reality a 4-barrel is easier to tune, cheaper to buy, and will get you just as much if not more power.[/quote]
Very well said. And, if the cast crank worries you, stroke your already bigger displacement small block, getting a forged crank...also, the more you stroke it, the more inches :) and torque...oh, and get your mind out of the gutter...lol