The Pfluegers are fine and back in the 50's and 60's were considered to be one of the better reels to get. Although you can find out what line weight the lines are by weighing the first 30' of them; however, you are much better off simply tossing them out and getting a new line that matches your rod or rods. The reason you are better off getting new lines and tossing the old ones is the old lines have been loosing plasticisers since they were removed from their protective packaging. This means the old lines will be prone to cracking and failure of the line coating. A new line will not have these and will also have the newer, far more durable and slicker line coatings of today.
The best thing to do is buy one or more (if you need different line weights for different rods) weight forward floating line in the size that matches your rod, and the best way to do this is at a local fly fishing store (usually called a fly shop). A fly shop has knowledgeable people working in it that the local Wal-mart doesn't so you will get what will work best for you, not just what happens to be on the shelf. The difference in price between a shop and the discount store is not very much when in comes to fly lines.