New to V8's. 340 or 383?

360
Put in some better pistons, 202 heads, moderate cam, good intake and it will out perform a 383 built similiarly and cheaper to build. You will need to change the trans with 383 as well which will add another 1,000 or so dollars.
Heck, if you bore a 360 .040", you can tell people that you have a stroked 340!