Kirby lux
Your wrong on rainbow belt. The e2 gold silver and black first edition are the exact same size. I've literally had 15 rainbows and the belts are the exact same. The e2 black later model belt is like 3 inches wide. You can heed caution if you wish but brand new e series belts are identical to kirby.
Kirby and royal belts have to rotate to fit on the fan. The rainbow and the eureka are pulley to pulley with no rotating of the belt bearings won't have nearly that much tension.
Like I said you'll get people saying otherwise but the belts are the same.