comp 262 vs 268

On an otherwise stock 318, you will be happier with the 262. Given your stock compression ratio, low RPM cylinder pressure will suffer with the larger cam. So then will low RPM torque and throttle response.

I'd run the 262 with anything less than 9:1 actual compression ratio.

The bottom end of your engine, so long as it is in good condition will easily handle any amount of power you'll make with either cam, a Performer, 600 CFM carb and headers.