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No, wiring will be different. It is not only the gun but everything that makes it go boom. From fuses to cable lenght to etc.Don't need a new motor. Just swap out the cannon as it's not a part of the motor.
Excellent photo showing that the cannon is inside the fuselage with only the barrel extending forward through the engine V.Bf 109 with the engine removed.
The engine had very little to do with the cannon, I believe the tube through the engine would take any barrel under 70mm in diameter.
Once you have planes in production with the 30mm MK 108 the parts needed to convert an older fighter become more available. Either from the factories or scrounged from wrecks (landing accidents would be the most convenient.) Parts would be the gun mounts, charging system, firing system, ammo boxes/chutes. How much of this type "stuff" could be fabricated by good armourers/mechanics I don't know. Might depend on the base they were at and access to equipment.
Going by that diagram the 20mm ammo drum is above the gun and behind the firewall which makes sense given putting it in the wing would put it very close to the main landing gear where you cannot afford to weaken structure but now two people say it is in the wing...