not easy to find a stroke kit but all you need to do is replate the cylinder and get a new crank. i think I have one lying around. I think I also have a 60 cylinder but I'll need your measurements from the top of the cylinder to the bottom. there were 2 thicknesses avail. You'll need to have your head machined for proper squish though.
The motor you have is the Morini S5 it has many of the same parts as the Cobra.