Rob,
Unfortunately the Cartridges of the World varies pretty widely in whether and which cartridges have detailed drawings, but for each chapter there is a table that has a more-or-less complete set of cartridge and case dimensions...expecially base and neck diameter, case and overall length, etc. This may help.
As this part of the thread has rolled out, I was beginning to think along the same lines as my far Southern buddy, JD Steele that a case based on the .30 Krag/.303 Brit pattern and as long as you want or could find would make a nice "brass panatella" for you.
A CASE you might look at is the .444 Marlin. This is availble off-the-shelf and has that case size, but is probably a bit shorter than you would like to see. I would feel good about this in a high-wall, but that is JMHO, of course.
One nice thing about working with that high-wall, just about any cartridge of the time was available in it at one time or another, so if it will go in the barrel you use (keeping to the small shank dimension) it will be "right" for that rifle.
As for further harming the collector value of the original barrel, if it's messed up already, it's messed up. Campbell's book showed some salvage techniques for peening metal back into place, and of course there is always the welding possibility, and if you wish to "restore" the rifle, that possibility is there. BTW, dod we ever establish exactly which profile this barrel actually has?
Froggie