Not positive but it does seem that a few have done that. Maybe try searching into the old post under oil coolers and see if something comes up.
I would imagine it would cool better, however that can be a double edge swrod at times. If the temp are not real high and you do not block or control them somewhat, you could find the oil getting too cool and having too cold of oil is not better. Also, unless you are moving-the oil is not going to be that much (maybe a little due to the extra capacity and the radient heat from the increase surface area) and if stuck for a long time in a hot area, not going to help all as much as one may think.
If you are moving, with exception of a very few areas, the oil coolers are not really helping greatly for these engines can take quite a bit and were designed to run allot hotter than many would think.
All said though, having a cooler can not hurt as long as taken into cooler temps are accounted for by either some sort of thermostat or use of a cover to block such.
All said though, I am pretty sure that others have put two BD Coolers on and you should be able to find some old post of such using gthe search feature and doing a little digging.