I know that the original MM preamps used an LM4250 opamp which has a maximum supply voltage of +/-18V. So with a single ended supply you could run that opamp with 36V max as RobbieK stated above. But as RobbieK pointed out, the caps would need to be checked to see what their working voltage ratings are.
I'm wondering where is the other battery is going to fit. It's not much room in the control cavity unless you cut out a space in the wood. The ones I built myself I run at 18 volts for more headroom. But I put them all in Stingray copy basses that I didn't mind chopping into the wood to make the other battery fit.