Somewhere in this thread (I can't find your exact quote now), you say that you suspect that engines are modeled as one big block. There are threads a year or two old here that deal with damage modeling, they show that damage models are more sophisticated than you believe them to be, there are inf fact several small components modeled in each engine. I think there are only two or three planes in game (P-39 being one of them) that have a simple, old damage model like you describe. So if your Buffalo's engine loses power after only 2-5 bullets, that means one of those bullets hit an important component.
You also say that the engine on a Buffalo seems to damage differently than the same one on a C-47. Are you taking shots to the engines from the same angle for both planes? I.e., are you chasing a Wellington or Val with the C-47 to take hits from the front?
"The bullets that are consistently killing the Wright Cyclone R-1820 engine on the Buffalo series are 0.30 caliber bullets being fired from anywhere from 50-300 meters distance, and they cause near instant engine-stoppage or serious power loss, regardless of where they hit. We're talking about bullets that make small holes and which might not have much power on them when they hit."
Don't rifle-caliber bullets have plenty of energy even after traveling 300m, never-mind just 50m?
"all bullets are treated as being incendiary"
Sorry, you're simply wrong here, check the fourth post of this thread:
http://forum.1cpublishing.eu/showthr...hlight=belting
"Since damage modeling is an art, it seems to me that IL2's developers have made planes that were notably vulnerable in combat for any reason excessively vulnerable to any sort of damage."
No, just look at the Zero. Famously fragile, and in-game the early-war Zeros are particularly easy to set on fire, but have you ever had a damaged or stopped engine in a Zero? Fragile fuel tanks in wing-roots, but super-tough engines.