Heeeps of advantage.

I actually had a MC16 bottom end and gearbox in my MC18. The '18 cyls go straight on, '18 heads go straight on '16 cyls too. The electrics will swap straight over, as long as you swap the whole system. And if you get the PGMII electrics, you will have to use the '18 carbs and mounting rubber cos the PGMII has a throttle position sensor attached to the carbs.

You end up with a MC18 engine except for slightly different gear ratios.

Worth the work. Hell, even the '18 heads, carbs and electrics are worth the effort over the '16 stuff...

My 2cents
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The Chopster