ricasdad,
Gunparts corp has new .38/55 barrels available. The caliber is a classic and far more "rare" and thus more valuable from a collecting or trading standpoint. Also currently, factory cartridges and loading components are readily available.
Is there something wrong with the barrel on your rifle now? and why the .30/30? they are a dime a dozen at any pawn shop. I am not knocking the caliber, I have several, but why change from the .38/55?
I think that it would be cheaper to just buy a .30/30 than to convert to one.
Personally, I ordered one of the GPC .38/55 barrels and replaced a worn, battered, and "plain" .30/30 barrel on a '94, ( post '64 model) specifically for shooting cast bullets in. the operation was a success and I don't see why the reverse wouldn't work as well, but again, I must ask why?