If the bottom end of your motor is in good condition and you are just trying to get the bike in running condition, rebuilding the head and cylinder is just what you need to bring the engine back to life. In some cases, if the cylinder walls and the piston is not scratched, you might be able to use them with new piston rings. However, I recommend you get a new piston and rings. You might even want to get an oversize piston and have the cylinder re-bored and honed from a machine shop. The benefits are two fold, not only you get a nice fitting Piston and Rings, you will get more power from the bigger piston.
Don't forget to use a new exhaust valve seal, or the engine will smoke!