enlarged gas tank.
 

Just learned from several on line data sources that the 6.3 W109 used a larger gas tank than any of the other versions of this model...27.8 vs 21.7. Since the body shell is likely identical, I would imagine that they are interchangeable, which would not be a bad thing for the 4.5 given the lousy mileage that that US only model gets due to diminished efficiency of early smog compliance measures. Indeed, the pre 1968 6.3 got about the same mileage as the 1972-3 4.5 model!

Thought '68 was the first year that the 6.3 existed and then MB really began to produce and then sell them '69-'70-'71. I had a '70 for about ten years. As I remember I got 10mpg on premium the entire time I owned it. Have no idea what size gas tank it had but I have the FSM someplace and will look it up when I get a chance.

How about posting a pic of the Silver Cloud.

both interchangeable and hard to find at a reasonable price. -cth