I'm far from an expert but this is what I think I know.
If the propeller spinner is not equipped with the center locking bolt, then it's a 250 or 270.
If you have this locking bolt, then it's a later lower unit but not necessarily the same upper units.
If the transmission oil fill port is located near the 2:00 O'clock position just above the shift mechanism, it may be a 275 or later.
If this is a single screw helmet pin, then it's a 250/270?
If it has the double bolt helmet pin, then it's a 275 or later transmission, of which may not necessarily tell you which lower unit has been installed by someone.
The 275 exhaust outlet housing extends a bit beyond the main gear case.... whereas the 270 exhaust outlet housing does not protrude much beyond.
The 280 has exhaust from the anti-ventilation housing instead of a cup behind the propeller.
And if that isn?t confusing enough, I think I have a 280 drive with a single helmet pin.
