I don't know if Baileys sells them but a 272 will bolt on there too...all of the Husqvarna cylinders will need a different carburetor than what is on the 670. The 670 uses a vacuum hose from the side of the cylinder to the top of the carb. The Husqvarna's are a through the base of the cylinder..through the manifold to the carb vacuum.
there is a used 670 piston and cylinder in the ebay stores if it has'nt been sold for 75.00. if you want a new piston a 266 or 268 husky will work if you cant find a 670. good luck.