I do not know the exact layout, sized ETC but if you want to keep the tank, why not just pop a hole in the tank large enough for the starter to poke into and then glass in a sealed tube to reseal the tank but still allows the starter to be inside the sealed tube protruding into the tank?

On my Lightning, Comp-ARF has the wing tube going right through the middle of the fuel tanks.

Just a thought...

Beave