Treb,
I'll have to defer to others with more knowledge on the Repro .410s. I've seen only multi gauge sets of 28g/.410 on 00 frames (28ga frame). I have read threads on the Parker forum about .410 only Repro's, but don't know if they were 000 or 0000 framed guns.

When you look down the CSM .410 barrels, you can detect the blended tapers, much like many other barrels in other gauges. While most guns have two tapers and then the straight (constant o.d.) section, these .410 barrels have three tapers and then the straight section. Personally, I think they could/should have tapered them down more quickly and shaved another 1/4 lb off.