I have seen this many times on EBay, they always say its a customized hearse. I dont think its custom at all (except the normal coachwork), the coaches in Argentina, Australia or someplace like that just look like this. I have a pic of a late 60s Buick that is very similar.
I have thought aboug getting it just to see if there is anything written on the back about it. Either way, it is a very cool '58.