Elvis (and anione else who doesn't know about Les) DONT MESS WITH LES!
While you shouldn't harass any mod or admin here, Les is far less leinent than the other mods or admin here. (which are generally lax, though they can still bite if provoked) Most forums have (and, arguably need) a "hard @ss" mod that keeps order, and deals with a proportionally higher number of idiots on the sight. (and those who may know what the're talking about but don't know when to shut up or cool down) Responding in kind to a mod's attack on you won't help, argue respectfully, otherwise you may just be falling into a trap. You (Elvis) haven't had any problems on here yet and are a decent guy, and you're fairly new with no dissipliary offenses. (same for me) So don't harass mods (there's no good excuse) and certianly
DONT MESS WITH LES! Respect their Authoritah!
But bact to the topic at hand, the Il-2 was a good attack plane with incredible damage resistange and pilot protection. The liquid cooled engine was no more volnerable than a radial in this case due to the placement of the radiator and the amount of armor. Hoever, the rear gunner was of limited value with a decent armament but very volnerable, and most importantly the ship had a volnerable belly mounted oil cooler that could be easily disabled by rifle caliber bullets. (which a radial engine requires as well)
As a tank buster I'd say it was probably better than the Stuka though. (though the Stuka was more maneuverable it was lacking in other areas, and when weighed down with heavy cannons it's performance was definately worse and much more volnerable, but it was a dive bomber first and foremost and decent in this role, but having a radial engine would hae helped)
The Il-10 was excelent, fast, no more iolcooler volnerability, better all around performning, and more capable than the Il-2 in all respects, but it came a bit late to be useful.
On the P-39/P-63, the M4/M10 37mm cannon was not a particularly good anti tank weapon, though not as useless for this as a MK 108 and probably better than most 20mm guns, it wascertainly less useful than the MK 103. But the M9 cannon fitted to the XP-63D was an excelent gun for this role. The M9 could penetrate 60mm of armor at 460 m opposed to the M4's 20 mm. See:
The WWII Fighter Gun Debate: Gun Tables
The radiator and oil cooler of these a/c were mounted directly under the engine with air intakes in the wing roots and exhausting along the belly aft of the engine. This was a fairly protected location with the volnerable area made as small as possible, but not much moreso than the P-40. (nd in general the P-40 was a tougher a/c as well, at least compared to the P-39)