The 9551 is the new, i think is Brushless motor inside of it. So if you want to use a Low-Profile servo in your sedan, have to find a 9550 from an online store that still has one in stock, or get teh KO-2413 low profile servo or wait for the new 9551...
But if not, like samstheman2 said, the S9451 regular sized servo would work great! and itsonly $80 and imo is teh best servo out for that specs!