Stock height 4x4 Duramax swap??

[Edahall]

I just checked a company called Duraburb that specializes in these conversions and they indeed add a small body lift (like the stock Duramax equipped truck) to provide clearance for the Allison tranny. If you're dead set on a Duramax and no body lift, you might look into a 4L80e tranny (like what was used in a Duramax van), a manual transmission, or creating a transmission tunnel which would be cool.