This fake 3D sprite ship approach sounds like a really bad idea to me, sorry. Just use a 3D model instead, if you keep the polygon count low it will even render faster than 6 sprites because the engine and the culling algorithm only have to consider one entity and you don't have to update angles and the like.
"Falls das Resultat nicht einfach nur dermassen gut aussieht, sollten Sie nochmal von vorn anfangen..." - Manual
