Your Peugeot's original cups are probably thin walled. If so, they won't work with the 3-series spindles commonly used for 68 mm bottom bracket shells. You'd have to screw the adjustable cup in so far that the lockring wouldn't have enough threads to engage. If you use your original Peugeot cups, you'd probably need a 5-series spindle meant for use with 70 mm Italian bottom brackets ...if you can find one in the right length for the particular crankset you want to use.

Since 3-series spindles are more common (by far), I think the easiest way to do this would be to scrap the Peugeot bottom bracket cups and use cups that aren't thin-walled, like the "Action" branded ones Harris Cyclery is stocking. Then you could choose your crankset and find a common 3-series spindle size to make it work.