I have a Wesson and Harrington BC with an additional 38-55 barrel. I have had no problems with the chambering on the 38-55 barrel and the bore is .379. I can't really give you any advice on the H&R barrels other than from the info I have read and that is that you might need some adjusting or reaming done to get it to work for you.
As for accuracy, the 38-55 is VERY accurate....unbelievably so, as a matter of fact. It seems to be a very forgiving cartridge as for loading and accuracy....the darn thing just shoots great with several different powders and charges! By comparison, it has taken me some time to get a "perfect", or close to perfect load for my 45-70 barrel and I'm still working on it.
Recoil: HA HA!! It is like night and day! One shoots like a light loaded 30-30 and the other kicks you like the devil.
Reloading cost: 38-55 brass is a little cheaper than the 45-70, not much. 38-55 brass is quite a bit more scarce than 45-70 brass, however, Cabela's sells it regularly. You're certainly not likely to find once fired 38-55 brass at a range either.
Obviously you're going to use less powder in the 38-55 which leads to a little savings. I only shoot cast bullets from mine for now and I can buy 100 38-55 bullets for roughly what I pay for 50 45-70 bullets. I guess you can get your calculator out and try to add that all up.

Recommendation: Get both! (that's what you were looking for, wasn't it?) I tend to really like the 38-55 and even if I got a barrel that was a little overbored or under-chambered, I'd get it worked on and work with it anyway. The results should be worth the trouble. Of course, look at the links that Quick posted too. Maybe if you ask someone who got a crappy barrel, they may tell you otherwise.