Maybe I've learned a good lesson . . .

This is the TWO problems I see:
[1] You have a heavy car with a small-ish engine.
[2] Take the 318, rated at 230 hp. And you mess around with cams, heads & get a 10% increase in hp. That is 23 hp. If you started with a 440 & did the same, you get 37 hp more.

If you had a light car like a Dart, then moving on the 318 would give you oomph you could feel.

Many parts/devices that increase HP are just power shifters: they take power from the low end & move it to the top end. With a heavy car, this can turn it into slug status.

I would put money into a larger engine. Even a bone stock 440 would be more satisfying that a hotted up 318.