Thanks for the input. I think, and could be wrong , that later models of the LMC1200 came with the OC-12 rear end. I dont think there is that much weight difference between the Clark 4 and the OC-12. That said I believe the frame is substantial enough to take an OC-12. There is zero difference between the forces placed on the frame from the transmitted force going through OC-12 and a Clark 4....the transmitted force from engine to rear end is identical other than whatever friction losses may be incurred. I appreciate your thoughts/opinion etc but what I really need is to hear from someone who has actually done this.