The car is being built as a low budget street/strip car, mainly for cruise nights.
The parts are what we have laying around, hence the 400 and auto (and Aspen).
I asked the parts guy and the trans is a B body, so are the headers as well as the oil pan (again, a deep sump Milodon).
The trans crossmember and mount are the /6.
Looks like this but with only one 'ear'
Mount will only bolt on the trans one way, and only fit into the crossmember one way. The tube section isn't as long, it's flush with the rubber and the rubber is solid urathane.