I also suspected that, but I checked both of my .65 Sportsters. They are both older versions, but just had "A 65" stamped on the right lug. Not a long set of numbers like he has, so I am not sure if what he has is a serial number or product number. Mine were made when K+B was still in Downey California and have the needle valve on the carb. Thats why I gave him a list to choose from.
Jollypopper, the Sportster series engines have a muffler that is a long and thin and is a two piece design. The mounting bolts go through the engine case, then through a seperate mounting flange and then into the muffler chamber. The Sportster engines are not by any definition a "High Performance" engine. They are however, very long wearing reliable engines. Feed it a high castor based fuel, 5-10% nitro and most importantly, prop it like a 4-stroke. These engines will produce lots of torque, not high RPM's. I have said for years that the .65 Sportster would be the ideal inexpenive engine for a Senior Telemaster or Senior Kadet. Its perfect for a big floating trainer thats not supposed to go fast!
If you try to push RPM's or mount it on a performance or 3D airplane you will be disapointed. It is what it is, a good long lasting reliable engine, not a fire breathing monster.