I've just done this exact job on mine and it wasn't too bad at all. I made the curtains from fabric I got via John Neal (member on here). Ask him where he got it, or I can. It's a really nice double-layer material. I didn't go for the ready-made ones as they use crimped laths, which the originals don't.
Just be sure to mark exactly where the curtains and tapes meet the drum and cut your new ones to the same length. I glued them with Evo-Stik, readily available in the UK. You could use most of the Zorki 4/4K guide I wrote (in the stickies) and ignore the bits about the flash-sync switch etc, the rest of it is very similar to a 4/4K.