You could just do what I did a year back and place the A4000D into any tower case like in this picture that I just took of my setup:

The Video hard drives are located in the smaller tower to the left of the main tower that has the A4000D in it along with a Cyberstorm PPC.
It has worked really well for me. and was fun to do.
The drawback with using an A3000T is that you loose all the AGA features that the Toaster 4000 uses including the color wipes.