TimC and Dnaer has said it all,

Yes I have the 70 OS and I put it as far back as I could on the mounts, leaving room for the fuel lines and the throttle control, Basically just placing it as far back as the frame would allow it was perfect, you can put the radio gear anywhere in the wing saddle and you should be right around the 4.25 - 4.50 balanced area, If you don't want to add weight you'll need to cut out a pop hatch behind the wing to balance yourself from 4.75 - 5. anything. I took off my 3" nose spinner and put the Battery behind the wing.


Good luck,, have a blast