I have been all over this forum. Most of the time I've spent on here has been in the Joes2006 thread and those related to it. I don't recall ever seeing anyone mention a dual head setup.
Although I haven't built my machine yet, I'm sure you could probably have a dual head machine if the machine will support the added weight. I don't think the 305oz. steppers will be the problem.
Here is the problem: The size of each duplicated cut will be limited to the spacing between the router heads. Now, you could make a wider carriage to spread the routers apart more. But then you would limit your travel on EVERYTHING that you choose to run on the machine.
What is the outside envelope of your cutting area? If th eprofile you're cutting is fairly small, you may be able to do it.