Gallahad:
I have a 45-70 barrel (non ported and no tamer), I also have a couple of rifles in 45-70. It is a great caliber for bear and moose, but the recoil can be rough using bullets over 350 grains. Recoil is pretty stout for anything other than factory 300 grain loads. But then again if deer is all your after the factory 300 grain hp will do just fine. I have taken bear with the 45-70 and it is effective! I always get a good exit wound and they never go far. It hits like a sledge hammer, knocking most to the ground. I keep my shots within 100 yards and never have a problem. If I were hunting deer with a 45-70, I would go with a moderate load in a 300 or 350 grain Hornady bullet.
Just a thought, but have you ever considered the 7-30 waters?
The 7-30 waters has all the power you need for deer and the recoil is easy to handle. I use mine for all around use on the farm. It does great on deer, coyote's, fox and the occassional wood chuck. I used to use a 223 barrel for coyote's, fox and ect., but anymore I just leave the 7-30 barrel on, I like it better. I have not used it on bear and would choose a different caliber for that, but in a pinch it would probably due just fine, with good bullet placement. Accuracy in my 14 inch barrel is great, it shoots as good as most of my rifles. Brass is easy to get and you can always neck down 30-30's.
Just my two cents worth!