I'm in the process of doing a tranny swap on my truck. It currently has the 4R70w. I had planned on running a ZF5 from a 99-'01 SD, which from research is great on the length. I had one located fairly close, but it ended up getting sold before I got to it. The next closest one I can find is 7 hours round trip. However I found, reasonably closer, a ZF6 tranny from an '02 SD. Problem is if I went ZF6 the tranny is quite a bit longer than what I'm set up for.

Now that you know the back ground I need opinions on what to do about the suspension, should I decide to go with the ZF6. Option 1 is to relieve suspension pressure cut the torsion bar x-member up/reweld it in the middle for clearance for the transfer case. Option 2 would be to remove the torsion bars and X-member in favor of coilovers in front. Last option would be to do a pre-'79 SAS with adaptors up front for 5.135 wheels.

My question is related to option 2. I'm thinking this would be the easiest route. The LCAs appear pretty robust on these trucks and I'm sure the lower shock mount could easily support the weight of mounting a coilover. Then you'd just have to cut off the stock upper shock mount and weld in an upper hoop, reinforce it, and get some 2.0 coilovers to fit. What do you guys think?

 

Option 3 leaf springs. Currently in my opinion the frames on these trucks weren't rated for coil overs. I think if you did run that route you would need to run a brace over the top of the motor to support the extra weight and keep the frame from twisting under load. I plan eventually to switch to a four link setup and coils with a cummins as a power plant. But I need massive reinforcement to do the swap as I want it to last long term.

 

Option 2 only if you make new lower a arms the shock mount was never intended for it support the weight of the vehicle and it will snap off.