Falicon cranks reckon they can stroke a two stroke press together crank for less than $600

http://www.faliconcranks.com/cw-list.htm#twin

Depending on the stroke amount depends on what you do with teh cylinder.
If just a few mm stroke increase (like 3mm) you can get away with cylinder base spacers and relying on head gasket thickness to accept the now negative deck height.

To really get the best out of a stroke you could do with the NSR150sp cylinders too....
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NSRless again...