I have a 91 w250 with the 4500 LBS front axle. Now I know there are 2 different casting numbers and I have vented rotors. I really don't have the place to disassemble my truck and leave it apart to find out which casting number I have. Also I've heard that if you take a 1 ton chevy rotor from that year and drill out the stud holes that would work but I still not sure what I should do. Has anyone ran into this?