Hello Hermosil
yes, my records show the Viking was, in fact, a 720 base (the second one).
Yes, the name 'Viking' is a good clue too smile

I failed to mention that boss and blade holder design will also impact.
Some blade holders are 'dished' more to compensate for crank lengths.

I guessed economy of price was paramount in this case.
I think this was the best way to explain things - the principles involved.
The caution - for all members - is not to produce an unsafe machine,
where the blades extend below the skirt.

I hope you sort it out.
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Jack