You may like this, Kawasaki Z1 6 cylinder engine.
For those that don't know, the Kawasaki Z1 is a 4 cylinder, air-cooled, DOHC, carburetted, chain-drive motorcycle introduced in 19724
cylinder. Together with the Honda CB 750 it finished off the British motorcycle industry, which was woefully outdated, the best it could do was
twin cylinder ohv engines.
The series of videos by Allen Millyard shows how he made a 6 cylinder engine from two 4 cylinder engines.
https://www.youtube.com/playlist?list=PLop2HGVepi07H_Y7iT2VtXaiWZYRIhowW
Very Nice
Seem to remember it being the fastest bike in the world in its day ?
A good mate has a concourse one that has had a nut and bolt restoration, They fetch serious money now aswell