MTK, I love what your doing here, I'm all for the idea of finding a gasser with performance/delivery that we're after.
The only thing that causes concern is the nose ring/hal senor problems and it's great to see you're making progress.
Still, the cut out for the sensor and the critical positioning of the nose ring due to the sensor mount still doesn't look like the optimal solution.
Couldn't help thinking that if you have access to a machine shop, why not try doing something like I've illustrated.
A smooth round machined collar thats bolted to the crank case encapturing the sensor/mount and providing a solid base for a traditional, albeit larger nose ring.
The width of the collar allowing plenty of flexibility for engine movement.
Of course I've draw it solid to explain the point... but it could be skeletonised thus saving weight, not to mention making it rather pretty.
And F3A guys love those pretty bits!
Keep up the good work and call me when you've machined a few. I'll have one.