Not owning a lathe is not the same as not having access to one. Surely there is one available locally (try your local trade school) you can use for the relatively short period of time you need to turn the barrel shanks to the proper dimensions, thread them and rough cut the chambers.

Incidentally, piloted drill bits are a very expeditious means of removing the majority of metal from the chamber area, followed by a roughing reamer (which doubles as a resizing die reamer, if so ordered from the manufacturer) and finally by the finishing reamer, which can be turned by hand, using a tap wrench to turn it with.

Whatever method you use, be sure to withdraw the drill or reamer frequently to clean off chips and to keep it well lubricated.