I had both upper and lower cracks. We (dealer and I) believe that the cracks at the top started first and when they completely sheered it cascaded to the lower which could no longer take the strain.

This happens at initial startup. The torque of this motor is on the ridiculous side and when one cylinder catches and the other skips a beat then the swings are enormous. This is why the 'skip-fire' mode gives me the creeps. It is a real strain on the frame. I have entered skip-fire twice and it is not fun. It feels like the motor is trying to leave the building!

I'm looking into adding an active oil cooler as well as some fans to avoid this. Motorcycle frames wrap around the engine while the Morgan is stuck out on forks which allow for much more flexing.

What's your mileage? Who cares. Is it practical? See #1. What happens when it rains? You get wet.