Shot peening the area of failure would help with surface hardness, but would be hard to do without damaging bearing surfaces.
This is something I've been thinking about. If a cam is going to fail ... that spot is exactly where it would.
There is 1/2" of shaft between the bearing journal and the first lobe on the cam ... I think enough room, if you cut into the journal a little, to machine in a rounded corner without sacrificing overall strength of the shaft.
Follow that up with shot peening and I'd think you'd be good to go. If I were building a multifuel engine, I think I would spend the time and do this.
But THAT is just a band-aid.
The real fix is finding out why that (perhaps those) cam bearings wore.
Unfortunately, I don't think there is enough data to gather from just ONE failure to suggest its a manufacturer or fleet wide problem.
Let me get the rest of this thing torn down and see what there is to see.