There's not an exact measurement for "too much" play in your cutlass* [sleeve] bearing. I'm a play it safe kind of Manatee. Any play at all is too much for me. Vibration, hammering or hum while in gear and/or under way, or a distinct clunk when shifting could mean your cutlass bearing is about due for a change. But, if you already have her out of the water and accessible, Put some firm pressure on it and see how much it moves. If in doubt, it's probably better to change it while she's up on hard than find out on the water.

Some say it's a simple task. They've obviously never seen Max in action. Here is someone who knows how to do it, and is not all flippers.

BoatNotes

Manatee Max has Morse Cutlass Bearings in stock. If you don't see the size you need give us a shout and we'll see if we can find one for you. 

https://manateemax.com/morse/

*Cutlass is a proprietary eponym from the trade name Cutless of Johnson Duramax Marine.