Really don't hear much with people retrofitting AL units to these trucks.
I had kind of planned on it, but I think I've been talked out of it. Your plans are different than mine, but here's what I heard from pro's, and what I thought of myself.
Aluminum radiators tend to "pop" the seal at the tank and core. Any stress placed on this joint (imagine grabbing either side of the radiator and twisting in opposite directions) will only increase chances of it failing. Yes you have rubber cushions, but I wouldn't rely on them to absorb any and all flex your truck might dish out.
Most new trucks (or cars) that are using AL radiators use MUCH stiffer frames than what our trucks have. You only need to crease your roof once to know that anything tying both frame rails together has to flex as well...the core support is one of them.
I really like the cooling capabilities of AL radiators, and will likely install one in my car, but the STOCK AL radiators I don't think, are up to the task in a truck. If you went custom, all welded, it would probably hold up better, but a "standard" stock radiator should hold up to more flex than an aluminum one, even if welded.
Some people may not see it as a problem, but having been told to stay away from retrofitting a stock AL unit to my truck by a "pro", and knowing the problems associated with the stock units, I am more than likely just going to get a 3 row "stock" replacement for my year truck.
No real solution for you on a smaller radiator, but FWIW, my manual trans 350 cooled FINE with a 2 row "tall" radiator that wasn't in real good shape. A 3 row that was shorter, with no tranny fluid run through it, might work ok for you, although increasing the "thickness" isn't as effective as increasing the front surface area. (making it taller)