I did the same thing...
I ran a Lincolin single fan for a while.
Was really big and drew alot of power.
Then I swapped to a dual set from an LS1 Camaro.
Fit the rad perfectly with only very minor trimming.
I hooked the primary fan to a thermostatic relay
and the secondary relay to the a/c clutch.
Worked VERY well, both fans did... however I had trouble keeping a
thermostatic switch that would live any length of time.
I have done this mod on other vehicles too and found the switches were unreliable.
Anyway, after replacing switches a few times and getting really PO'd at it,
I just put the clutch fan back.
I can say without a doubt, this is one mod I have done to my SD truck that
DID make a SOTP difference. Must have picked up 10 rwhp easy.