Although kits may be available, rebuilding is quite a mech-savvy job. It's either a complete rebuild, meaning that the engine is taken into atoms, cylinders re-honed, new pistons+rings, (putting them together is a form of art on its own), rebuild the heads, meaning that valves must be set-up, the list goes on. The easiest option for you is either go to a shop that SPECIALIZES in rebuilding, and they'll do it for you. Trust me it's still better than ashamedly bringing a motor in the shop and let them puzzle it out (more hours more $). another option is install a fresher or rebuilt engine, and it possibly saves money on the long run.
A rebuild is serious matter, you can't cut corners