Thanks group, it does seem that the lower shaft has risen maybe 1/2" but still appears engaged to the oil pump drive cause it will not rotate.
Yes, the original distributor was in the car and running fine when suddenly stalled due to losing spark.
Any idea why/how the lower shaft could rise bout 1/2" like that? In essence, the lower shaft is free to wobble easily now, after soaking heavily with PB blaster, but will not rotate.
All three dizzies have comparable dimensions and all will drop down only so far after appearing to engage the lower shaft. They seem to engage or lock into the lower shaft but are about 3/16" shy of allowing the distributor locating pin to reach the locating pin hole in the head.
I am thinking trying to pull the lower shaft out of the head and re-think what might be going on.