Actually 70 and 71 Imps also had the antenna in the windshield. The 72-73 were only Fusies with a power toy.
http://www.fuselage.de/imp69/69imp07b.jpg
http://www.fuselage.de/imp70/70imp02b.jpg
http://www.fuselage.de/imp71/71imp01b.jpg
I know, brochures may be a bit off, I´ve yet to see a 69-71...