I was not aware anything was available, I believe all those parts have been sold, there also would be no cross member because the Alpha used the 4L80 trans.
There is however some adapter plates to adapt the Dmax to the original motor mounts but some other mods need to be made as the engine sits higher on those adapters, they come from some guys that are sticking Dmax motors in old chevy Impalas
What transfer case is that? that is an interesting looking adapter.
Also how are you controlling the Allison, that is a mechanical 6BT yes?