OK the only difference between the VC-125 Mark I and Mark II is,the height adjuster is different and the bottom part of the handle.
As seen here:
Height adjuster.
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Mark I (Without plastic handle on)
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Mark II (Without plastic handle on).My Mark II (that I'm restoring) currently has the Mark I handles on it.I'm soon to get the right handles.

Bottom part of handles and handle catch.
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Mark I
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Mark II
Yes they both have decompression valves.
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No they don't have brass bush Gudgeon pins.The conrod bearing is what I know as needle bearing.Not sure if that is what you were asking.
The VC-125 Mark III is a completely different looking mower altogether and a lot rarer (If that is a word) and I'm still hoping I can find myself one.
I hope this has helped.

Here for a good time,not a long time.