Craig,
I took a look at one of my Ryobi's that is still tore down ,because of no oil. The cylinder is held on with two screws. If you remove the cylinder, leaving the piston attached to the case, you will see the mounting flange at the bottom. You can drill and tap the back of the flange, about 3/4th inch in from the end. There is a lot of meat here and the hole will go directly into the transfer port. Use a 8-32 tap or one that matches you fitting. A DuBro pressure tap fitting would with a 8-32 thread. You can do it on either side and you won't have to disassemble the mount,carb etc. After drilling,tapping and installing the fitting with gasket or sealant, clean the filings and oil the bore. With the piston at the top of the stroke,align the ring gap with the pin in the ring grouve. Insure that the gasket or sealant is in place on the top of the case flange. Compress the ring and slip the piston into the cylinder. Seat the cylinder and install the two retaining screws.

Dave