I followed much the same idea as you when i came here,
Some models theres big differences, for example 2007 690 SM is same as 2008 duke . The 2008 enduro is a completely different bike compared to 2008 SM/duke.
Dirt on the 2007-2008SM/duke,they dont even look like it can be dirt aggressive.
2008 enduro is setup to make your dirt fun with 650cc power.
Newer SMC/enduro models can be identical except suspension/wheels/fuel tank/s, maybe seat.
It would take a bit of your personal study time to figure out depending on the year/s.
older than 2003 -old design LC4
2003-2005-kind of similar(not inlcuding 660 motors)(carby motors)
2007-2011-kind of similar(fuel injection introduced)
2012-2014- kind of
2015- and up some spec changes here and there , didnt study it out.
Hope that helps ,
current -2007 690SM