They work, but your timing will be slightly off on the cylinders that have different lines. You can use either lines on either engine, but you SHOULD use ALL of the lines from one style on the other, and that includes the pulse timing adapter for #1 if your switching from 6.9 lines to 7.3 lines, unless you replace the #1 7.3 line with one from a 7.3 powered van. Mixing and matching lines on the same engine will not produce the best results, so really you should try to keep the sets together. Also when you cross from one line set to the other, you may have just a little bit of trouble threading the nuts on since the lines are more or less perfectly bent for the engine they are intended for, but mechanically you will not have a problem once you do get them on there. As for finding a replacement line, I'd say just buy a new one. Yea, they are pricey but you only need to do it once. Check and make sure your line clamps are in good shape, as those little guys save you a bunch of money down the road.