Setterguy,
I would not cut them off shorter than the 24 inches you already have. If the gun needs to loose weight, thin the tubes some more out past the halfway point rather than shortening them. They will handle better and point better than the shorter barrels as well as giving you a longer sighting radius. That's something that nobody mentions much around here, but it is important to a guns' accuracy that will be shot mostly offhand. If you shorten the barrels or lighten them too much, they become whippy and harder to shoot well. You need some weight out front to help stabilize the offhand shooting. Much of the final weight will depend on your body makeup and overall strength.

If you are slightly built, then too much weight will make it difficult for you to hold up and shoot the gun, but if you are a big stronger man, then too light a front weight will make it very hard for you to shoot the gun because your muscles need a given amount of strain on them to become more solid during offhand shooting. If all you were doing was shooting over a bench, it wouldn't matter.

We all have our ideas about what's right in balancing and designing. I'll tell you now that I am primarily a hunter who builds guns, and if they are too heavy to carry in rough brush all day, then I don't care for that. But, I still want enough weight forward to make for good offhand shooting. You will have to compute your gun's overall weight to match the loads used and your over all ability to absorb recoil. Recoil bothers some people alot more than others. Good luck with your project, and I still think that the 45/70 is the right choice for your gun. Bob H.