Thanks Sam for helping me with this one... check out lwtracer.com if you havent yet!
1g and early 2g motors are similar enough that you can swap them
you need the stator/flywheel/rear intake manifold/thermostat/rear header off the bike you're swapping it into.
late 2g (dual plug) motors can be swapped into earlier models and just leave the second set of plugs disconnected
early motors cannot work with dual plug ecus (you would at least need to swap heads to dual plug)
gladius motors swap right over into late 2g. same idea (dont use the second set of plugs) with early 2g. and stator/flywheel/manifold/etc for 1g.
3g is basically the gladius motor so same as gladius, fits anything, needs parts swapped for 1g, sparks get left alone for early 2g.
1g and early 2g (03-06) is the sweetspot since they can take ANY motor from any bike with some adjustments