The Thunderbird trans is electronic, probably an A4LD overdrive. The same trans as in the Ranger/Explorer/Aerostar.

The 3.8's are SLOW, unless you have the Eaton on top.

The diff is a thing of beauty. It's an 8.8 center with independent suspension like a Jag. Better than a Jag, really, because the brakes are outboard and parst are cheaper. It comes out as one large piece with subframe and all.

I was going to use one in my f100, but I decided against it because I'm still using it as a truck and I was worried about it's loading limit.