More or less a straight swap if you exchange the whole engine unit, 
including accessories (UK versions).

I've replaced two 1600cc engines with the 'pancake' 2000cc engine 
(carburetted).

Some thought had to be given to the wiring in the region of the  regulator.

The later engines had a  sturdier gearbox. It's preferable to fit the 
appropriate gearbox. If you retain the gearbox for a 1600cc engine, a later 
bellhousing and starter motor will be required.

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