i'm pretty sure your stronglight spindle is that crazy campagnolo-type. So your standard japanese parts won't fit, even though they are also square tapered. it's a different kind of square taper. So you could go with campy. Or go with a 5-series japanese tapered spindle. A 5-series will say 5N, 5P, stuff like that. Most standard spindles are 3-series (3N, 3T, etc). You need this different one because the bearing races are 2mm further apart, otherwise your bottom bracket lockring won't fit right.
and yes, i would love your px-10 stem. So much so that I'll PM you about it too.