Interior 550 Maranello is from 550 Barchetta Spider Elite. Original model HW 550 Maranello had different seats but in reality 550 Maranello had as an extra option available sport seats just the same one like in 550 Barchetta. 
Engine and lights also from 550 Barchetta Spider Elite. 
Front and side air intakes come from 550 Barchetta. Wheels of 550 Maranello were closer to original ones for this car so I did not change them.
Other models similar to Ferrari 550 Maranello: 550 Barchetta Spider, its successor 575 Maranello, 575 Superamerica, 575 GTC
Engine Ferrari 550 Maranello Hot Wheels and 550 Barchetta Spider Hot Wheels 1:18
Engine Ferrari 575 Maranello Hot Wheels Elite and 550 Maranello Hot Wheels 1:18
Engine Ferrari 575 Superamerica Hot Wheels Elite and 575 Maranello Hot Wheels Elite 1:18
EngineFerrari 575 GTC Kyosho and 550 Superamerica Hot Wheels Elite 1:18