Williams is scale length but has the wrong numbers for NH. It has a three axle truck but uses PA-1 side castings. The real EP-5 has three axles but they are not evenly spaced. You can get the K-Line side castings from Lionel and you can modify them to match the Williams truck. There will be some offset because the casting reflect the uneven spacing of the axles. I'm not sure if the K-Line has the correct uneven spacing or not. We're talking about 1 scale foot, aka 1/4" difference. I find the correct side castings look better with slight offset on one axle than PA-1's with the axle matching the bearing caps on the castings.
K-Line has better/more accurate detailing of the shell. None of them will have the correct cab interior because the vertical can motors are going to wind up inside the cab. The Williams roof details are off but the price is hard to beat. I got a Williams EP-5 for about $125. Adding in sound, control and coil couplers added another $100. Sound set isn't quite a match for a real EP-5 but the horns on the roof aren't a match either. Current Williams units use the E-7 pilot casting which doesn't match the prototype. Since it's my Railroad and not the New Haven's I left the "wrong" one in place because I think it looks better. I still fiddle with this changing minor parts as I find them. Since I only paid $125 I don't mind kit bashing the engine.
K-Line made three versions of the scale EP-5. Conventional with a classic horn/bell, K-Line's own sound set, and a full blown TMCC/RailSounds/w cruise. If you find one a a show or on-line make sure it matches what you are looking for/expect.