I've no idea if it can be found on here but many years ago it was posted here.
A guy took a CB125 single, removed the head and block and blocked off the hole.
He made a new hole in the front of the motor and grafted on one cylinder from a DOHC 4 cylinder 600 Yamaha.
This gave him a DOHC 175 single and not content with that, he supercharged it.
OK guys, lets see who can find it as I'm off to bed.