GT6 OD question

["Edward Hamilton" <hamilton@ptd.net>]

I'm going to take a peek at a '72 GT-6 later this week.  According to the
current owner, during a telephone converstaion, he claims the OD to be a "J"
type.  When I responded that I thought the GT-6 to have been fitted with a
"D" type, he tells me that he had it specially built??
What am I going to look at here -- what "other" tranny/OD's would fit in a
GT-6?

Thanks in advance,
Ed Hamilton