Detach engine gears

Hello, I’m new here and introduce myself briefly, hot Dirk am 1966 born and has been driving a Camaro Z21 Iroc Z for 21 years. Since my baby Öil loses ( crankshaft seal to the gearbox ) I want to expand the engine including the gearbox. But have not done such a repair yet. Has any of you ever done such a thing before? I would be grateful for a few tips and hints.