45 colt in a 'tender?

The 45 Colt has been doing the job quite nicely for a long time. If you do load with black powder or smokeless equivalent I suggest using pure lead bullets. At BHN-5 pure lead performs admirable at the lower velocities. I am using pure a pure lead penta hollow point in the 44 special and 44 Russian and in both the pure lead bullets expand nicely. I think we also have the same bullet design in 45 but I will have to check to be sure. Even if not a hollow point pure lead still gets my approval.

About the 45-410 barrels I have found that if you use a longer case they can shoot bullets pretty darn good. Shooting a 45 Colt in that long chamber the bullet has quite a long jump to the rifling but with a longer case like a 460 S&W not so. I believe even longer cases can be made from 303 Britt or 30-40 Krag but I have not tried that, I have though tried the 460 S&W cases with good results.
I am with you though in that I would prefer to have a 45 Colt only barrel than the combo barrel but if I found a 45-410 for a great price I would have to do some serious thinking before turning it down.

Likely will depend on what dies you have. Some are not open top. I think I used 45 acp open top RCBS dies. 45 Colt or 454 Casull dies will work as long as the extra case length can be accommodated by an open top die. By open top I mean the type that you can remove the de-cap rod from where the de-cap rod is larger than case diameter. This allows the extra case length to pass through the top of the die. All my older RCBS dies are this way. For instance I can size a 45-120 3 1/4" length case in my old open top RCBS 45-70 2 1/10" length sizer die.