I'm actually starting to doubt the fact that his car is "the" ss396 convertible. It was sold to him back in the 70's or early 80's, just as a parts only car. He was told it was the ss396 but I don't know if anyone has ran the numbers, but it did have the 396 when he bought it, as far as he remembers. He then raced it, circle track, so the doors are gutted and welded shut, the quarters and rear tail light panel are dinged to snot and there's stuff welded onto the frame where the radiator support used to be. I know it at least is an "SS", Glove box has the Malibu SS stuff, plus he admit he knew at least that. The firewall tag is still there, but I could find no vin tag beyond that, I swear one was on there last year, but I could be wrong and I swear reading Z16 on a tag before, I honestly never heard about the Z16 nickname until the last couple weeks, I've never really messed with too much restoration/numbers matching stuff beyond the deal with my uncle's SCJ big block and simple Ford part numbers, so here's some info.
Here's what that tag reads:

SF 65-13837 ATL 5397 BODY
TB 792- K-K PAINT
2MS
That is at least what rubbed off when I did the old trick of holding a piece of paper over the tag then rubbing a pencil over it.