The current CB's in the 20" barreled version are basically the same as the CB II/24" barreled ones, except for barrel length. The strictly .38 version is the CBC. It also has a case color frame instead of a blued one. I have both, a CB in .45 and a CBC in .38 Spec., they both have been almost flawless in operation.
Unless you just HAVE to have the case colors( why I have mine), the standard CB will work just fine and leave you a little cash left over to do some smthing if you want an action job. Like most lever guns, they can be OAL sensitive at times. None of mine have been, but still they can be from one unit to another. We have two .38 Marlins, the aforementioned CBC and an 1894 CS( round barrel carbine). The CS has fed anything we've put in it..........................Buck