Ok, here is what i measured a while back. You may have to cut off and weld the part on the radiator support where the 2 pieces meet and it has the uneven meatal.
23.5" wide or so x about 3" thick x 13-14" max height. For the height you will most likely have to cut off the uneven pieces of metal unless you go with a radiator that is 1.5-2" thick. In that case you may be able to get away without cutting the radiator support.
summit part #'s griffin-gri226185-x, gri256185-h, gri-2-26185xc,gri226185h,gri256185x. Most of these options should work. These are the ones that came the closest to my measurements.
I was going to try and get one without a filler neck and run a remote res. with a filler on that or a suge tank as some call it.