"Let's see, you take a perfectly good running gasoline fueled engine and then you ruin it? <G>"

Maybe we have different definitions to what Ruined is.
Adjust Carb, Add weight (replace plug & ignition parts).... run gasoline again.... I fail to see the ruined aspect, seems like it was a gas engine that can be setup for glowplug and reset back to gas. The Glow works without having to grind the mounts. As ruined as chalk ruins a chalkboard.

If what you meant is Degraded rather than ruined, that depends on your scale of standards and priorities
----Weight, Interference, Cost of Fuels, Power
Would you lose 2lb if it cost 10rpm drop? What about lose 1oz if it cost 1000rpm drop. Clearly there is some point in the middle where it is RPM cost effective to lose weight. And that is a personal opinion/preference. Same with LBs vs FuelCost.