I have tried both, the tapered and squared off. I did switch to a roller cam and I am hearing that there is a difference in the shaft/gear on the roller cams. Checking into that now
At this point post a picture of your broken intermediate shafts.
It does not take much in the oil pump to jam it up and cause the intermediate shaft to twist the tip off. There is a lot of stress there when the pump stops and the camshaft is still turning. It can be a tiny but of trash easily missed during inspection that gets stuck between the rotors of the pump. If you don't find anything wrong with the depth of the distributor revisit the oil pump and the pickup. Look carefully in the bottom of the oil pan for anything that feels gritty.