RE: Engines dying randomly?
"would both tune properly and run well on the ground."
Sounds to me like that "properly" may very well be in question. Two different engines. The only comonallity is the tuner. I would suggest that perhaps the tuner is tuning the engines in too lean, so that when the prop unloads, and the engines pick up rpm, they are starving; i.e. tuned too lean on the ground.
Les