Deejay will know the answer for sure, but I don't recall there ever being a 2 hp engine on a 17" SB45. Those 6 cubic inch engines only went on the 14" machines IIRC. The 17" models had engines of 2.5 hp and more.
Your engine is old, being silver - probably 1960s, and probably a 60102 or 60202. I suggest you preserve it in case you ever acquire an SB45 it belongs on. The engine is as much a classic as the SB45 itself.
