Engine dilema.. 318 or 360?

Bigger ports on X, J, or better yet 308s on a mild cammed 318 will tend to be lazy on throttle response, especially running street gears. I'd slap a set of freshened up 302 heads on that fresh 318 short block to get a torquey street runner AND decent mileage.

That said, if you're willing to give up the additional gas mileage the smaller motor will give you over most 340s or 360s, 20K on any Mope smallblock is nothing, relatively speaking and additional torque and/or power is already built in. Freshened up J heads with a modern cam tailered for the car's weight and gears on that 360 will definately put a smile on your face.