What do you mean moving the engine to the rear reduces armour. I know a lot of tankers think having the engine in front in some APC or tank models improves protection but in reality it just improves the crews ability to get in an out of the back. And engine is not the same as armour. It is much softer than armour… even a solid slug from a shotgun will go straight through a car engine and with a 16 cylinder engine there are a lot of tubes carrying fuel that can be ruptured… in a hot engine that will almost always start a fire as you can’t use safety foam in fuel lines like you can in fuel tanks.

The insignificant level of protection for the pilot created by having the engine in front of him is no great loss. Armour around the Pilot therefore also protects the engine behind him so it performs the same dual role as it does when the engine is in front and the engine armour protects both the engine and the crew.
A turboprop engine is also much smaller than an inline piston engine, which was a serious for WWII Russian fighters like the Migs where big long relatively heavy engines dominated the design and not in a good way. It also frees up the belly of the aircraft to allow a big gun if that is wanted without the problems of a propeller in the way.

What I mean is the structural armor, that such an arrangement, with the wings on the sides can afford. This was really the key innovation in the IL-2. Its what made it considerably lighter than the equivalen conventional warplane that was armored to the same level.

About Engines – your average engine, if you took out all the fancy gizmos has not gone as far as people believe in the last 50 years. But obviously, we’d need a better engine on “our” IL-2. (or our IL-10)