One problem with the used lines besides possibly leaking at the crimps will be the old-rings where it screws into the radiator, unless you've got Jiffy tite connectors there too...... I did not on my truck, but I've got a late 400. I think the earlier trucks used Jiffy-tites on both ends.
I tried getting o-rings once, and the universal o-ring box that every parts store has had o-rings that were too thick. I ended up going to the dealer, who had them in stock for cheap, but I think they've been discontinued now. I suppose you could probably get some at the hardwater store, but they may not survive as long if they're for household plumbing.