Completed the conversion! I ended up using some old casings because they're just impossible to cut without a purpose-built cutter. I ordered a cutter, and when it arrives I'll re-do the cabling (which I need to do anyway).

Fortunately the R443 FD is flawless with the 2303 shifter; that was a main concern going into the project. Now Just some fitting adjustments and I shoudl be good to go.

I'll post a pick of the finished product, but it doesn't look much different than the pic above.