I am not even sure what I was searching for. But happened on a website the other day. I could not believe what I was reading. So, I gave this gunsmith a call.
He has been taking sxs shotguns and converting them into double rifles. These are not elephant stoppers. But they will handle everything except the largest bears with no problems.

We chatted for a time on the phone. He sleeves the sxs and bushes the firing pin. He regulates the gun and installs iron sights. He does all this in about 60 days and charges $650.00 if you supply the shotgun.
He prefers to chamber them for either 45-70 or 45-90. Exactly how many chamberings he is willing to work with, we did not discuss. He states that 45-70 can be loaded to modern lever action pressures.
Here is his website:
http://www.angelfire.com/sd/rgs1/work.html His name is:
Daniel Ruppelt
31049 ERS Rd.
Springfield, SD 57062
605-369-2636
Pete