Just looking by googleing rpo codes it looks like the code is V12 but neither of my trucks have that code but they both have the tube and fin style cooler.
My 1999 C2500 has the tube and fin cooler but no V12 code on what I believe to be its build sheet.
This just came to thought. Maybe its a 8600 gvw thing that gives them a cooler and being 4wd. Both of them are 8 lug 2500's.
Mine is 8 lug 8600 gvw - but only 2WD.