Bike-Maker's thread is top notch stuff, and I seriously considered using SD axles. The heavier setup, better brakes and access to SD series rims (prime used parts these days) where all very tempting. The rear axle would of course have to be swapped to match. But in the end, I scored an entire parts truck for under $700 CAD, which is about as cheap as these axles come in my neck in the woods. Wreckers still want almost twice that just for D60 front axle. And yes, I too heard aware of that 3.31 dana60 axle ratio, although I've never seen one in the flesh. The front frame mod is the biggest hurdle of the job and I'm not looking forward to ripping that section out of the donor truck, let alone getting it into mine. But now that I'm this deep, I'll probably follow through with it. As for spring rates, I seem to get as many different answers as I can find sources. So far I've seen: 2200, 2600, 3000 and now 3400 for the flat springs intended for D60 solid axle front ends. I read on one thread here at OBN that 2600 was too soft, so maybe go with middle of the road 3000lbs?