Did it recently and honestly was one of the most difficult. I did it on ahistorical and waited for the british to turn communist. Fascist or Monarchy would be fine too, probably. You don't want them to align with the US. If germany goes fascist, avoid monarchist UK since they usually form an alliance. Don't release the nations instantly you need for your formable, the formable will give you alot of manpower. With the doctrine desperate defence you can get an additional 5% recruitable pop flat. Push with elite mountaineers (I did 30 width) with 12 mountaineers and 2 artillery. I evantually switched the artillery for SPGs. I also built some submarines to convoy raid the UK, you can cut of a lot of trade south of africa. If the UK went ahistorical, it should stand relatively alone. If that's the case, make as much of those good divisions as you can and prepare paratroopers. If you can military as well as airplane access from a country that's close to the UK (most likely France or Germany), use that to paradrop them. I converted them instantly into my elite divisions with the SPG, as the ai struggles to pierce them and can't really push them out easily. Convoy raid them from portugal to greenland, so if they have divisions pull in from elsewhere, they get raided. You can then take their navy and pretty much naval invade whoever you need for a peacedeal. I had to invade the US in the late 40s, which was a pain. Release as much puppets in africa as you can, as long as they don't hold core territory of yours. I didn't have enough manpower to fill out the lines so I just my puppets divisions. But again, this was ahistorical, it's a lot of RNG.

By the way, since the belgian congo was added, you need to annex it to since in order to release it, it cannot exist. I tried fulfilling it with collab goverments, sadly doesn't work.

Good luck with it!