One option appears to be pull the tranny cooler off, build a tank about four to five inches thick and the same rectangular dimensions of your radiator, and mount it about three inches forward of the existing radiator. Mount the trans cooler on the side of the cage you build to house the fuel cell. Looks to me like with the trans cooler off to the side, you would have enough forward space to do that. Looks like you would have to put the fan out front to keep heat off the fuel tank.
Dimensions of 22 x 20 x 4 give a tank capacity of 7+gallons? You could build it to what ever size you need to alter ballast. Just run more or less fuel.