The simple cassette or magazine feed is not so simple.
If you want a ground attack Battle in 1940 forget the Taurus engine. More Beauforts were lost due to engine failure than the Germans shot down in the early days.
Make more Merlin VIII engines as used in the Fulmar, or RAF equivalent (no Coffman starter), ust change the gear ratio on the supercharger. 1080hp for take off on 87 octane fuel. The British thought so much of the Taurus engine that they bought 200 P&W R-1830s to use instead but the ship carrying the engines was sunk on the trip over and the British figured that bad engines were better than no engines.
It isn't the "kit" that slows the Battle down so much as the fact the fuselage was deep enough for the bomb aimer to lay down under the pilots seat.
A semi automatic cannon (AT, AA or field gun) uses the recoil of the gun to open the breech block and eject the fired round. Springs are compressed for run out, to move the breech block back into position (blocks moved either vertically or horizontal but movement was perpendicular to the axis of the bore), and to cock the ejector spring. When the loader tossed (rammed) the new shell in with his hand/arm the rim hit the ejector and pushed it forward, tripping the release for the spring that slammed the breech block into position. Now please note that the gun barrel had returned to firing position with the breech block open and will sit there waiting to be loaded until it rusts. Yes you can use the energy of the recoiling gun to cock springs in a feed system.
just about all automatic guns (Madisons and a perhaps few others excepted?) have the breech block traveling to and fro in line with the barrel. Barrel may or may not recoil depending on design but the Breech block travels reward, extractor pulls the case from the chamber, ejector simply knocks the casing clear of the bolt/breech block face and out of the gun on the reward part of the trip. Bolt/breech block spring is compressed and at the end of the travel throws the bolt/Breech block forward and the bolt/breechblock picks up a new cartridge from the feed system (box.drum, belt system and pushes it into the chamber.
If you take an existing AT semi auto AT gun and try to turn it into an automatic gun (or just fit a loading system) you need to design a ramming system that will take rounds from the magazine or feed and push them at the proper angle the proper distance with enough force to trip the extractor/ejector catch and release the breech block. You don't have the weight of the bolt/breech block pushing the cartridge with a strong spring behind it. Yes you can install springs and arms and pushrods but it seems a bit complicated.
The Molins company specialized in cigarette making machinery. Their MK I machine was tweaked to make 1000 cigarettes a minute by the end of the 1920s and they were building the MK VI machine in the mid 30s. SO the Molins company was used to making things move at high speed using levers and arms.
In the end what have you got?
Vickers had a 25.4mm gun and cartridge that was functionally identical to the 25mm Hotchkiss AA gun. That is to say with in a few percent of gun weight, rate of fire, shell weight and velocity. Granted the French 25mm AT gun was somewhat more powerful but then you are going to need a heavier gun and with loading system add on it is unlikely to fire as fast.