I would not remove original windows. Would you consider storm windows if energy efficiency is an issue? But if there is no dissuading you on this one just post online thru your local classified, Craig's list or similar. Can you post some pics of the Windows?

If you can't see through them, they may be lead.

Get a reclaimation shop in your area to check them out and IMO old windows need to be replaced even if you spend the money to have them copied they are very poor insulators and storm windows are not much help in reality. You could just google lead windows and see if you see anything similar to yours for starters