340 X heads advice

OP, we have no idea what you are doing with this engine and heads, your rear gearing, nor what is in the 360 block for pistons. If these are stock, low compression 360 pistons and you want to put a moderate to large cam in it with X-heads, you will have an engine that will tend to bog at low RPM's. If this is not a race or strip application, you may not be happy. In that case, you may be a lot happier IMHO with a set of EQ heads with the smaller chambers.

So some more info on the application is needed to help you along.