You were correct with the A, D, and J being vehicle mounted sirens. They are definitely not bad sirens to start out with. I got lucky and my dad found one in a factory where they were installing a crane and got it for free. You can sometimes find them for free, or pretty cheap on ebay.
There used to be both a Model 5 and a Model 2 at the former Downtown Oswego FD. The sirens were left there to rot until earlier this year. The Model 5 was turned into a mystery siren, but it was taken down earlier this year. The Model 2 was taken down 4 days later. I don't think that's a custom hou...
Man, all sirens really need a light bar, then I'd know when not to sit there for 5 minutes hoping for the siren to go off. Anyways, I remember watching this on TV when people were getting hyped about it.