I recently bought a used Sundowner seat for my 2005 XL. Owner stated that it fit a 2004 200? Sportster with 4.5 gal. tank, which is what I have. I have noticed other used seats of the same type with the stated Harley part number...51507-04. Seat seems to fit OK, but other seats pictured do not look the same as the one I got. Either the metal tongue in the front is shorter, or the keyhole slot look different, or the vinyl wrapped underneath is different. How do I know if I have the correct part? Don't see 51507-04 anywhere on the seat.