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Consider that by the Battle of Britain, most air forces admitted that rifle-calibre machine guns were not powerful enough to shoot down modern, all-metal airplanes. Even 8 MGs firing .303 struggled to stop German bombers during the Battle of Britain. Most air forces scrambled to perfect 20 or 30mm auto-cannons to the point they were small enough and reliable enough to install in wings.

Another option was installing motor cannons that fired through the Center of the propeller shaft .... aka: motor-cannons.

OTL Russia and Germany used motor cannons extensively during WW2, but hardly any other combatants.

OTL Russia installed 20mm motor cannons in Lagg 3, Yak 1,3 and 9. Russia also flew hundreds (thousands?) of American-made Bell P-37 and P-63 with 37mm cannons. P-36 Airacobra had a unique engine installation behind the pilot with only armament, drive shaft and Propeller Speed Reduction Unit in the nose. The 37mm cannon only fired through the final PSRU. Russian pilots loved P-37 and downed hundreds of German airplanes with them.
Meanwhile Yaks were powered by Klimov V, inline engines that had been developed from Hispano-Suiza V12 engines. Klimovs' 20mm cannon lay between the cylinder banks and only fired through the PSRU.

Germany installed 20mm motor cannons in the thousands of Messerschmitt 109 single-seat fighters that were equipped by DB 600 series engines. Since DB 600 series were inverted V engines, the cannon nestled in between cylinder banks - below the crankshaft - and only fired through the PRSU. MG151 cannons downed thousands of Allied airplanes.

Hispano-Suiza built the first MC during WW1 when they installed a Lewis MG (.303) to fire through the PRSU of a V8, HS-36 engine that was mounted on a SPAD fighter. A later version included a 37mm cannon, but that had to be manually reloaded by the pilot (1 shot at a time).
By the onset of WW2, HS had developed V12 engines producing up to 1,000 horsepower and sporting HS 20mm auto-cannon firing through the prop hub.
The French built about 900 Moranes with HS motor cannon, but they did not participate in many WW2 battles.

WI other engine manufacturers could have modified their engines to accept motor-cannons?
Could you install a MC in a RR Merlin?
Consider how many different Merlin variants were developed and most of the changes were to induction systems.
RR Griffon?
Allison V-1710?
Radial engines ..... consider the transfer case on the R975 radial engine installed in M18 Hellcats. The transfer case displaced the drive shaft down to the outer circumference of that radial engine. If you install a motor cannon in any other radial, the prop shaft - and cannon - will stay on the centre-line but will be displaced up or down until there is sufficient clearance between cylinders. Try to picture the small Pobjoy radials built during the 1930s.
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