With the restrictions others added here about multi-coil systems, it can
work.

I've done the opposite on my boat; I got a nice tach cheap but it was
8000 rpm max, so I run it in "4 cylinder" mode and it reads 4000 RPM max.
A few stick-on numbers inside and it Works For Me.

Some tachs allow you to select 4,6 or 8 cylinder.. If you OB is 4 cylinder 2
cycle, couldn't you select 8 cylinder and that would allow for the 2x

--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?