The best way to upgrade to a 70cc cylinder is to replace the short block so you keep the cylinder and crankcase together. The 54 and 57cc models did not use the bearing insert on the PTO side, the 60, 70, and 82cc models all used the insert in one form or another. To try and match a 54cc crankcase bottom/oil tank with a 60, 70, or 82cc cylinder would require some intricate modifications to the bearing insert to get the halves put together and sealed.
With so many of the 63258/84080 insulators out there, no need to make something up, just get the right insulator and gaskets.
Mark
With so many of the 63258/84080 insulators out there, no need to make something up, just get the right insulator and gaskets.
Mark