The CH-54 and S64 engines are at different heights for the reason stated above (3 degree mast tilt to the left). The mast is tilted forward on the Crane however, it has an inbuilt 3 degree forward tilt.
The CH-54 did have firewalls between the engines, but the S64 has the firewall extended over the top of the engine (but nothing on the outside).
There were two models of Crane built, the CH-54A (essentially equivalent to the S64E) and the CH-54B, which only had a Restricted Category TC and was never placed into commercial production (but became the S64F). To the casual observer, the most significant outward difference, is the S64E has single large mainwheels and the S64F has smaller twin mainwheels.
As is typical with Sikorsky products, each derived considerably from previous, or contemporary models. The CH-54A (S64E) utilized a rotor system derived from the CH-37A. The CH-54B (S64F) utilized a rotor system derived from the CH-53A series.
As a result there is very little commonality between the MGB, MRH and blades on the two models, which presents a challenge to anyone operating these machines. Although there are other differences, the other most significant difference is the engines; the S64E utilizing the P&W JFTD12-4A (4500 s.hp) and the S64E the P&W JFTD12-5A (4800 s.hp). Although there is only a dash number change in these engines, they are significantly different.
For the S64E total power for two-engine operation is limited to 6,600 s.hp.for takeoff, and 5,400 s.hp. maximum continuous.
For the S64F total power for two-engine operation is limited to 7,900 s.hp. for takeoff, and 6,600 s.hp. maximum continuous.
With derated limits like this, the machine has tons of reserve.
Sikorsky sold the the S64 Type Certificate to Erickson Aircrane in the early 90's and Erickson has been converting CH-54A's to S64E's, and CH-54B's to S64F's ever since. They have a very impressive operation and capability there, as they have to manufacture a considerable number of parts to keep this programme operational.