Instead overhauling, would you like to consider it to replace with 4G13 Engine? I guess the expense will be same.
4G13 is among more successful engines of Mitsubishi/Hyundai since 1980s. Specially I like its sound in 5th Gear crossing 80Km speed. The car become smooth like silk.
And if transmissions are Automatic with 4g13, then consider it blessing.