Got it. Didn't see it before.

Mark,

You're idea of bring the sensor in from the back could work well as long as you have the sensor oriented correctly. The air gap between the magnet and the sensor needs to be pretty close, say no more than 3/32". That will make drilling the hole a little trick. Re-timing the engine is easy since it's likely the sensor will be relocated. Looks like you have a syncro spark ignition since you can't see any advance rods in the picture.