This one makes you want to cry. The Hepburn is one of the stronger actions and will work for most anything reasonable. Don't think there was a Hepburn carbine, but maybe the factory would make what you wanted. My guess: The guy with the hacksaw turned a $2K-$3K rifle into something less than $1K. Would make a fine saddle rifle. Hope I am wrong. Pictures would be interesting.
Chuck 

P.S. Did Marlin have John Taylor add length to a similar barrel, then reline? Amazing work, bad memory.

Am guessing you are correct about the barrel length, though the muzzle is nicely finished, so was obviously turned. Indeed, is too bad what someone did. Makes one wonder if it wasn't fired with an obstruction in the barrel, which resulted in a bulge near the muzzle that had to be removed. Will never know. Like they say........... too bad our old rifles can't talk.

The saddest part of the shortened barrel is how nice it is, inside and out.

All is not lost, as it's possible to save the old Hepburn and restore much of it's value. I personally would keep the original chambering since it's most likely marked on the lower flat in front of the forearm.
I also have a nice original Hepburn in .40-70SS that someone lopped the barrel off of in it's early life. I took the gun to John Taylor and he lengthened the barrel by making up 10" of donor barrel and welding it on the existing barrel. Then he relined it to the original caliber and I reblued the barrel.
I now have a normal length barrel in the original caliber, which still has all the original markings! I paid $800 for the gun, and with John's usual magic he restored much of the gun's value at a reasonable fee.
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Yes........ have all ready had the discussion with JT about lengthing the existing barrel as opposed to putting on a new one. As far as cost, he tells me that it is pretty much a wash. The original is stamped 45-70 on the bottom flat in front of the forearm. 

Have also spoken to DZ Arms in OKC, who makes new Hepburns (along with C. Sharps). He offers a double-set trigger group, but stated emphatically that at $1000, it is not worth it and that a single-set trigger was never offered in a Hepburn.

Might be a wash to put a new barrel on it and chamber it to any caliber, but you wont get it at an even wash once you figure in the original rollstamps, caliber markings and serial number to make it correct. 
If it's just going to be a shooter, I'd still have it lengthened as it will shoot great when John is done, and be worth more than a newly barreled Hepburn.

So go ahead and make the offer, then let us know how things work out with that Heppie......