what did you come up with on this deal? if you want more tongue weight leave the two you have where they are and put your third to the back of the other two and add an equalizing trunion like what is between the two axles you have now. Your shakle on the front axle and spring will stay the same you will have to get an intermitiate spring set to put on the 2nd axle and put your rear springs on the 3rd axle. now your load centerline will be the centerline of the 2nd axle instead of the pivot trunion between axle 1 and axle2. thus moving your load center back about 18 inches or so and increasing tounge weight.