Todd- no heat issues running both in series then? Sounds like lots of capacity for sure. Where you live you need it for sure.
When I first swapped in the 4r I used just one Derale cooler with an 8" fan, appr 13" x 8" stacked plate cooler since it seemed like 99% of the "swaps" I read about this was all ya needed. First real 90deg day of testing it with at least s20 minute or more of 10deg incline on a dirt road (old stagecoarch route) w/o the converter locked in & being in 2nd gear most of the way I saw 200deg and I had to pull over for 20min to cool it down. Extremely disappointed.
I then plumbed in the SD cooler and the fan never came on again.
Eventually pulled the Derale cooler and just ran the SD cooler with the 4r.
Only run the SD cooler with the 6r and in the winter (like I mentioned) I run cardboard covering it. Just seems to work really well.
I have about 1/4" btw the cooler and the grill and about 3/4" btw the cooler and the radiator. All works fine cooling 600hp also although most of you know I'm having "length of service life" with the 28" wide Griffin radiators.
What Steve linked looks almost exactly like the SD. I'll probably have to go with that if I ever need to since old SD coolers are non-existant in my area...