Johnson 35hp impeller

[Doubles Shooter]

I have a 1978 Johnson. I'd like to replace the impeller this year. Has anyone done this? are there any pitfalls to watch for? I've re-built  a couple of Harley's from the ground up so I am fairly mechanically inclined. Any help will be appreciated. Thanks

[Rumrunner]

You are probably a very smart guy but my only suggestion would be to find a service manual...just in case.