The only thing to watch with WFP and leaded windows is that they are mostly on old properties and some of them can be quite fragile and its often just the lead holding them up.
I used to clean a very large hotel all with leaded windows, this was a very old place and you could fit two fingers into some of the gaps round the edges of the windows.
If your starting a leaded job for the first time I would take a close look at them up a ladder first to make sure they are strong enough to take a WFP clean, from experience, customers don't like pure water shooting into their bedroom at 60 PSI
Andy