I like the sound of a detroit 6-71, but not many bolts have an engine big enough to accept that much engine.
Someone on this board is putting a detroit 4-53 in their "big bolt". It's looking like a slick setup. He custom fabbed mounts, and you'll have to make sure you have a front axle that can hold that weight.
I don't know if one of the cummins B series will fit or not.
