I have just bought a ZT and when I bought it the prev owner said it used to have highline unit and he tried two head units...one looked like early 75 lowline unit, and the one it currently has is a CR80 unit. Neither worked originally as C0981 and C0391 were disconnected and plugs trapped. The red/green telephone wire has been pulled out of somewhere too. Anyway I don't think this had highline as pictures of highline head units I have seen have different plug connections. Any help as how difficult it would be to fit highline?