Just keep the 340 and put a 6-pak on it for visual effect, if you like multiple carbs. I have a 360 with the 6-pak in my 67 Charger, and it gets a lot of wows...a few non Mopar types have even called it a 440 6-pak. With the small block you will have a better handling car (less weight) and better gas mileage......(just my two cents)