After weighing a number of factors (time being the biggest one), I have decided to go with an Advance Adapters #716691-AA aluminum 2-core cross-flow radiator. It's built by Custom Aluminum Radiators in Kingman Arizona for Advance Adapters and I can get it in about a week. I probably would have gone with a Ron Davis custom aluminum down-flow radiator, however, they had at least a 30-day lead time to even get to the point of shipping. Here's a pic of the new Advance Adapters radiator:
The core dimensions for the aluminum cross-flow radiator from Advance Adapters are 17-7/8 wide x 18-1/4" high, so that will provide 326 square inches of surface area. As a comparison, the core dimensions for the existing Advance Adapters copper/brass down-flow radiator in my TJ are 17-7/8" wide x 19-3/4 high, so that provided 353 square inches of surface area, however, it was a less efficient 3-core design that was 2-1/4" deep, while the aluminum cross-flow is the better cooling 2-core design at 3" in depth. Some adapting and new brackets will need to be fabbed-up to use my existing down-flow shroud on the new cross-flow radiator, however, that is doable.
The remaining question is going to be airflow. Steve Roberts at Advance Adapters continues to feel that their 16" Spal electric fans will not move enough air for my application (they top out around 2300 cfm). Evan Austin of Backwoods Offroad suggests a 15" Flex-A-Lite Black Magic Extreme 180 fan which moves around 3300 cfm of air. However, the 18" Lincoln Mark VIII fan that Deri0953 uses with his Ron Davis cross-flow radiator wins the cfm contest hands down at 4500-5000 cfm. Anyway, based on Steve Roberts recommendation, I plan to initially start out with the new Advance Adapters aluminum cross-flow radiator and use it with my existing 5.9 Limited Grand Cherokee mechanical fan and fan clutch assembly and see what cooling improvements can be gained with that set-up. If that doesn't end up cutting the mustard, then I will probably need to look at the Black Magic Extreme 180 fan or the Lincoln Mark VIII fan.