The Mecoa site advises you can identify the .45 by counting the cooling fins on the engine case. The .45 should have 10.
By the way if you are a K+B fan you should spend some time at their web site. It is loaded with info and advice. It also has a very good question and answer forum.

All of the K+B Sportsters were Schneurle ported engines.
They are still in production and all parts are available. You can even get a replacement older style carb if you need one from Mecoa.