If they wanted a Sturmovik, WALLIES would need to start from scratch with a radiator surrounded by an armoured box, with an armoured engine bolted to the front and an armoured cockpit bolted to the rear, .... Continue building outwards. The secret to Sturmovik's success was a radiator buried in the middle of the fuselage and surrounded by armour.
As for guns, start with the Bell Airacobra's 37 mm gun firing through the propeller hub, then upgrade from there. Remember that most Messerschmitt 109s had 20 mm cannon firing through their prop-hubs. The cannon breach protruded into the instrument panel. 12.7 mm (.50 caliber) was the minimum needed to shot down 1940-vintage airplanes, while tank-busting required larger calibres.
Muzzle velocity is more important than calibre, with 3,000 feet per second being the minimum muzzle-velocity to penetrate late-war tanks.
Accommodating the cannon was a simple matter of a reduction gearbox tall enough for the cannon to clear cylinder banks, induction manifolds and exhaust manifolds.
All WW2 fighter engines incorporated reduction gearboxes. The challenge was requesting a centre-line cannon early in the engine design process. This would have required the British Air Ministry requesting cannons during the mid-1930s. Heck an inventive engineer could even have installed a cannon on a radial engine, just point the barrel between two cylinders and "skew" the reduction gearbox to line it up with the barrel (ala. tiny Pobjoy radial engine.)
As for cannon caliber, start with 37mm, then upgrade to keep pace with advances in tank armour. Keep in mind that you only need 88 mm cannons to penetrate glacis plates (front of hull) because all the other plates are thinner. It is especially easy to penetrate thin deck plates when attacking from above.
Rockets were far less accurate than cannons, which is why RAF Coastal Command fired rockets from Swordfish, Beaufughters, Mosquitos, Fireflies, etc. Rockets were best at poking holes in the waterline a of large targets: ships.
All those machine guns (installed in the noses of CC airplanes) were merely to distract U-Boat AA gunners.
Twould seem that Typhoons were best at destroying morale.
As an old "Desert Rat" once told me: "The worst thing is being shelled for days on end and not being able to return fire."
By late summer 1944, Germans were exhausted from being bombed, shelled, straffed, etc. repeatedly without being able to return fire.
Typhoons' second role was destroying the German supply chain.
This thread contains some amusing ex-post-facto explanations attributed to the latest and greatest technology. Whereas every retreat has seen roadsides littered with wagons, equipment, loot, etc.
As for the single nose-cannon on A-10s forcing the nosewheel off-centre .... Taxiing suffers almost nothing, while gunnery improves a lot.
