John, I cracked up after reading your last sentence above.
I found a battery for my digital micrometer and checked the width again. It's actually 6.224cm. Didn't want to take the valve stems out so measured from outside of V1 stem to outside of V3 stem. Width = 6.826. That measurement includes half the width of TWO valve stems. So I measured the width of ONE valve stem (one whole = two halves) and got 6.02mm (.602cm) then subtracted that to get 6.224cm. I agree John that I would have thought the width to be wider on the M5050 since the bore is .610". It is a bear to polish between the valve casings.