Hi, the single carb manifold already came with the bike when I bought it however they are fairly easy to make.
A lot of people burn off the rubber on the original carb boots and use those for flanges. It’s important that when you join the mandrel bends to join the two to join together that it’s in the middle and there’s no blobs of weld or anything as I’ve read stories about people starving a cylinder of fuel slightly.
Also it’s a good idea to keep the manifold short as you can end up with fuel pooling, icing and general poor fuel economy.
Ideally, the bands won’t be too tight either as fuel will hit the walls and pool there too.
I’ve also read that some people have used a 90 degree bend where the carb slots on so as the carb sticks out the side of the bIke due to not having enough space at the rear of the engine. This can also lead to starving a cylinder, usually the one nearest the carb as the fuel/air has to do a merry little dance to get to the cylinder.
I went with the vm34, parts are very easy to get, jets are in abundance and they are pretty cheap. I’ve had a few problems here and there with tuning it but that’s mainly down to my lack of experience with carbs. I’m very very close to having it perfect now and it rides great.
One other thing to remember when choosing carb sizes, the bigger the Venturi the more power you will have at the bottom end, sacrificing a bit of top end. And vice versa.
The throttle response on my 440 is similar to a crosser as it’s a big carb. I would be keen to try a vm32 in the future to see what it does to the top end.
Hope this helps in some way