I'm not sure if the 3AJ is compared to the 3tb as far as counter shaft location since we didn't get them. I just did a 3TB into a 43F. As far as the electrics you'll need a bigger battery which won't fit unless you do some remodeling of the battery box or get a Lith-ion or such battery, but those have their own issues. Ignition switch, a right hand switch for the start button, starter relay and harness , the 3AJ main harness is also needed for the extra starter/button wires. Not real hard to do as long as you have a complete setup to start with. The cdi may be different and may need to be moved, not sure on that though
Oil lines may need to be modded depending how the 3AJ ran them.
If the sprocket is offset like the 3TB motor then you need to find a way to move it over a little(8mm) to have it line up with the rear sprocket. I moved the whole motor over approx. 4 mm by shimming one side and moving the other side engine mounts. then put 1/8" spacers behind the rear sprocket to get it even closer.
For an ignition switch I used a Yamaha Viper switch, it has the start option on it just like a car, twist to start then release, no button needed, I really, really like it.
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