Looking nice Dion. The biggest problem with mixing parts is not getting them to fit but getting them to line up.
I'm taking a guess here as I'm not 100% sure but on the A F and later K models, the gearbox sprocket was about 5 8ths of an inch further out from the cases than the early Ks. The swing arms were cranked out further to the left to clear the chain and the top suspension mount was longer on the left had side to line up with the one on the cranked out swinger.
The rear axle was longer and they had a sprocket carrier that was wider to allow the chain to line up.
You need to check all your part to make sure you have the correct ones.
Your swinger looks like it's from one of the ones I mentioned above. Drop a plumb line down from the top left suspension mount to see if it lines up.
Sam.