FAIR WARNING:
Don't try to install the barrel unless you're a trained pistolsmith and have several hundred dollars of special tools, including a lathe, special barrel vise inserts, a special frame wrench with Colt "I" frame polymer inserts, and a very expensive tool set used to cut the barrel for barrel/cylinder gap, and to re-cut and lap the forcing cone, along with the special drop-in forcing cone plug gage to measure it.
The old gag of locking the barrel in a vise and using a hammer handle to twist off the frame is pretty well guaranteed to destroy an expensive Python.
If you need a barrel fitted, send it in to Colt and let the pro's do it.
Pythons are just too valuable these days to risk.