As Oren says your tripod choice along with the A 250-2 would support an elephant. That is the combination I use for my 20 x 24 camera with holder and lens that equals about 75 lbs. Get a smaller Reis head as suggested above and you will be just fine. I second the joy of the Ries spring loaded screw as mounting the 20 x 24 without it would be mean spirited and cruel and unjust punishment.
cool format 14 x 20. I like that ratio.