The two-piece bladder tank sits between frames 3 & 5. Frame 3 is about 1.5 ft behind the forward landing gear fitting, with frame 5 located at the rear landing gear fitting.
And then you have the 2 SUPPLY tanks after that which extend pretty much to the rear of the boot floor.
RFM Section 7 Manufacturers Data.
If your spectro is upset by the fuel system you probably won't be putting it inside a 135.