Hey, easy now! Don't you remember, Bullseye came out with the first trick anodized derailleur pulleys well into the classic era defined by this list. I wanted a set way back then ('80-'81), but just never got them. Finally gonna do it! (If the right size is available. Don Walter Tucson, AZ
As you are finding, all current derailleurs (AFAIK) use 5mm bolts, and you need 6mm. Campy is also 5mm, but Suntour was 6mm.
BTW, we don't talk about modern "trick anodized aluminum" stuff here! I'm not going to help you ruin the classic perfection of your Simplex!