Hello Jack,
What age are the lines?
I have recently refurbished a reel for someone who had some good quality lines in apparently good condition on the spools - As he was stretching one of them, it snapped. We tried at various points through the line and it could be snapped by hand.
Not meaning to rain on your parade, however it is best to question before rather than after the event

---------- Post added at 01:46 PM ---------- Previous post was at 01:42 PM ----------
I should add that the lines in question were around....16 / 17 years old and had been stored on in a dark dry place on the spools.