If your bearings are gunked up with old castor there may not be any play, they would be very tight. I just had to replace bearings in one of my .91s. The engine was given to me, it ran great but I could hear and feel the bearings. I use the engine anyway until one day I could hear the bearings in a fly by, that's loud!! When I opened up the engine the bearings didn't show any real signs of wear or being loose. That was the problem, just too much nasty old castor oil that was making them tight. RC-bearings.com and a couple hours of work and the engine is like new again. However, you can't just tell by looking. Once the engine is loosened up and run a little it will tell you what it needs, if anything. My first four stroke book was from RC Modeler magazines anthology library series. RCM is defunct but they still sell plans so perhaps there library is still going too?? You will have to do the google and check. The title is, A guide to O.S. Model 4/Strokes by Graham C. Rice. It's a very good, easy to read and understand book with good pictures. I even use it today on every rebuild. At this point I would just heat and loosen to see if there is any problem? No reason to go looking for trouble, it will tell you when you fire it up. Stock OS bearings are pretty loose when brand new in the older engines. You can also soak an engine in some fuel to loosen things up but I like to heat them up first.