Which cylinder heads do you recommend?

If I had seen the post, I would have jumped all over it!! Ok so question: I'm still new to this. Will 340 heads fit right on the 318 with the mopar valve covers? How much better performance will I get? I've read forums of people putting them on like that, but I'm hesitant due to lack of knowledge, so I figured just go stock and drive it. I don't want anything crazy, but if I'm head to head with a ricer or someone that thinks their car is the ish, I don't want to get burnt by them!