Originally Posted by SkyBound
Correct me if I'm wrong but I'm pretty sure the E4 hitch weight difference is only in the bars, meaning you can buy heavier bars and still use the same components if you upgrade trailers.
With the "Equal-i-zer" brand WDH 4-point sway control (some refer to it as an E4) the different rated spring bars are not interchangeable with the original hardware, a new Equal-i-zer brand WDH would have to be purchased. This is the brand WDH the OP is referencing.
The "Fastway" brand "e2" WDH also has different spring bar ratings available, but I'm not sure if they are interchangeable.