Does the points cam index mark on an ND advance unit point to the 1-4 or the 2-3 markings? (it can be assembled either way so wondering which is correct.)
There's some really good images on here of the correct position.....but I can't readily find them.
It won't run if fitted backwards...giving crude analysis to confirm
Finding out...install it however fitted, turn the crank to F on 1&4 (as that's indexed to crank) the cam should now be starting ramp to lift points of 1&4 set to fire those piston at the top of stroke.
The other, wrong way, it will be just starting to lift 2&3 with those piston at the bottom of stroke.