I had a 307 bored +.06 that I got for $100 for my first motor. I put a 270 comp cam in it and it did sound pretty good. Another thing you cold do is get some roller rockers. Put 1.5 ratio on the intake and 1.6 on the exhaust and this may give you the thump your looking for plus if you do decide to move up to a 350 the rockers will also work for that too.