For the cannon you could always go for Antony G Williams what if Orliken cannon proposal. Quoted Below.
"An Alternative History
To sum up, by the end of the war the Japanese had produced a gun which had a comparable rate of fire to the Mauser MG 151/20, but weighed less, had a smoother recoil push and fired more powerful ammunition. The main disadvantage was that it was inherently unsuited to being synchronised to fire through the propeller disk, so it could not be mounted in a single-engined fighter's engine cowling or wing roots. None of the improvements made to the FFL were technically difficult, and they could all have been introduced at any time in the gun's development history if the need had been identified.
By comparison with the early war version of the 'ideal' WW2 20mm gun discussed
HERE, the fully-developed FFL would have been very similar; the cartridge was equally powerful, the rate of fire much the same, the weight probably slightly less (no more than 35 kg) and the recoil effects easier to manage. The disadvantages would have been the inability to synchronise the gun (not an issue in British or American practice) and the probable inability to raise its rate of fire later.
Of course, the effectiveness of the gun would have been further increased by the adoption of lighter, more streamlined Ausf.C type M-Geschoss as proposed for the 'ideal' gun. Assuming a 105g shell with 20g HE, fired at 850 m/s, this would have a cartridge power score of 26, giving our uprated FFL a gun power of 312 and a gun efficiency of 8.9; significantly better in all respects than any actual wartime 20mm gun.
The SEMAG/Oerlikon Type L was on commercial sale, to anyone who wanted it, from the early 1920s onwards. Any nation with a reasonably competent gun industry could at modest cost have acquired the gun and developed it in the way described. In particular, the British were testing the bigger Oerlikon S in the late 1920s/early 1930s (including, interestingly, a belt-fed version). Had a British company decided to acquire and develop the Type L then, they could have had a highly competitive 20mm cannon in service for the start of WW2. By comparison with the Hispano Mk II, it would have been less powerful but faster firing, much lighter and more compact, and caused fewer recoil-induced installation problems. It also would have been available in time for the Battle of Britain."
I always have always thought that for an ATl it would be difficult to better this proposal to give any protagonist a 'Best Off' aircraft cannon in 1940 which was not ASB.