If there is no compression, you definately need a top end. I would pull it apart, and inspect and mic all parts and replace everthing that is not withing spec. You will need a factory service manual, available on egay and your local honda dealer. While you are at it, set the float level, clean the air filter and fuel filter (in the tank) and install a new plug. Make sure there are no air leakes in the intake track that would allow dirty air into your engine. This is probably what killed it in the first place. Normally, a top end will not wear out suddenly, rather it will gradually loose compression. Also, make sure the exhaust valve is clean and working properly.
good luck