Theres a small lip on the nikasil barrels that can be machined off to allow them to fit the earlier engine. Apart from that there is not a huge difference in the engines. Upgrading the breather on the heavy flywheel engine is a worthwhile mod. If you have the earlier engine you will also need the clutch and earbox to go with it unless you intend to convert to a light flywheel.
To be honest I prefer the heavy flywheel engines.
To be honest I prefer the heavy flywheel engines.

]..
