it is pistons

Stock crank and 90.5 instead of 85.5
82s would make 1835
94 pistons would make a 1916

So - basically "all" that is needed is cutting the case and opening the heads to accept larger barrels.

They all work on stock cranks. it is after that that the strokers come in to play

The other part is if you want to make the HP that goes with it.
cam, head work, exhaust, etc etc

have a look here

http://www.aircooled.net/gnrlsite/resource/articles.htm 

and have a browse through a few of the articles.

Just to clarify the typo 92s=1835 :kiss