Okay, I understand what you are saying about the star, although it seems that no shaving of the sides would be necessary if the brass all dropped in to the .45 cylinder okay. Anyway, I'm gonna play the naysayer here and explain why I don't think it can be done. First, with a .38 cylinder, like I told Jake I think the bolt notches on those are deeper than the .44's and '45's. So yeah, it could be done but who would want to knowing the bolt notches are very likely to get blown out, even if they knew it would still be functional. I had heard that some of the early .45 S&W Opentop cylinders had the bolt notches accidently cut to the .38 depth by Uberti and a lot of those blew out. Now, if it turns out that info about the .38 notches being deeper is not correct, then I withdraw my comments
And as for using a .44 Colt cylinder, 44 Colt brass is slightly longer than the straight portion of 44-40 below the neck. So you couldn't re-chamber the cylinder with the necked portion where it needs to be, the hole is already too big at that point. I think Uberti made some early OT's in .44 Russian. I know they were marked that way. If the cylinder was actually chambered for .44 Russian, and you could find one of those, now THAT would work for re-chambering! Otherwise a machinist would have to manufacture a cylinder from scratch (Hey Raven, how much would that cost?
disclaimer: I'm not a gunsmith! So if my logic is incorrect, let me know. Because I think a 44-40 OT would be way cool, too. And certainly no more problematic than a 45LC OT.