The LD340 isn't a copy of the factory iron intake. Not even close IMO. If you set them next to each other, IIRC, the iron intake with a 3/4" spacer is closer in height to an LD340.
If you have an LD340, RPM or Air Gap, run it and don't waste your money on buying any of the other two to test them out. It won't make a significant difference and is a waste of money.
LD4B is a great intake as well for the smaller port engines. I really like them on the late 360's as well.