The earlier igniter units were slightly different to the later ones, not in the way they work, but physically. If you look at the unit from the front, the earlier units had a rectangular lump sticking out of the potting resin on the front left hand side.
Any 270 igniter unit will work on any 270 engine, but if you use an 865 igniter on a bike with performance cams (790 or 813's), you will not get the performance you were hoping for as there is far more ignition advance required for the hotter cams.
