Snake is right,
The MH-53J "Pave Low" and the CH-53E are vastly different airframes. Not only does the 53E have another engine, but the airframe is quite a bit larger on the E model. The tail structures are different. The 53E has a tail which is canted 5 degrees to the left, as compared to the MH-53J's straight tail. The sponsons are different, and so is the Main rotor pylon. The blades are similar, but not exactly the same. CH-53E's have a 2.5 foot blade extender on the blades root end. An MH-53J would need to be a whole new kit.
MH-53J's are updated B and C models dating back to the Vietnam era. H-53A's, B's, C's and D's were very similar. They greatest difference between them was in their engines, all of which were variations on GE's T-64. The CH-53E was a completely different beast. Sikorsky "went back to the drawing board," and the whole aircraft was changed greatly. It got a third engine, plus a seventh main rotor blade. It was lengthened and widened, and it's tail was redesigned. All of these changes were to give the Marine Corps the ability to carry greater payloads.
The price paid was in maintenance to flight hour ratio. It takes more work to get a 53E in the air than any other in the series.
The CH-53E has a twin brother, which is the Navy's MH-53E. It has huge sponsons and provisions in the cabin for towing a sonar sled for mine detection. There are some rear view mirrors on the chin bubbles so the pilot can see the Sonar sled. Other than that, the CH-53E and the MH-53E are identicle twins. Academy's kit fuselage has provisions for both sponsons.
I think some people may be getting the Navy's MH-53E mixed up with the Air Force's MH-53J. But they're far from similar.
Sikorsky will be producing a CH-53K for the Marine Corps in the next decade. It will be much different from all previous 53's. It will be larger than the E model, with 7 main rotor blades and 3 engines. The blades will be of a new airfoil with sloped tips for greater lift and quieter operation. Much of the fuselage will be made of composites to make the aircraft lighter and tougher. GE is slated to make a new generation of engine which is expected to make over 6500 shp. It will have a "glass cockpit," and "fly-by-wire." It will have larger sponsons, but will do away with the big Auxiliary fuel tanks. Much of it's design will be focused at reducing maintenance, thereby reducing its cost of operation and increasing its flight readyness. None of this is top secret, I read it in Marine Corps Times.
Semper Fi,
Chris