Engine Identification question, dont laugh.................too much

[EightySeven550]

Hey all,
I am going to check out an engine for my SJ, as much as I know about my 550s I have no idea what I am looking for in Yamahas.

What markings indicate what engine?

Any help would be appreciated.

Thanks,

 

[michael950]

They are cast into the engines: cylinder on the sides (carb) and cases on the front left (by bendix - small circle on the flywheel cover).