Do you think I would get interference from my ignition battery if I put it in the same area as my reciever battery and I kept the leads on seperate sides of the plane? I guess I'm trying to figure out how far I can stretch the 8"-12" rule! I'd like to avoid having to put one battery on the engine box and the other in the tail. Any suggestions?

You may or may not get interferance. I personally would not take the chance. Keep your ignition system(including switch) as far forward as possible!

It's not a good idea to place anything associated with the ignition next to, or close to the Rx. Be safe, put all ignition parts up front where they belong. You may not have a problem, but then anain you may. Why chance it.

First it is not a good practice.
Second, I have had my receiver pack on top of my ignition pack against the firewall.
No problems at all. Just make sure that your system is healthy and well grounded.