This thread got me wondering has anyone tried an old school bus engine?? They make some odd balls out there that are big and then they are low geared and you can really rack the Rpms up on them. I once had a 350 V6 in an old GMC dump truck. That motor had huge low end torque with a granny 4 speed and a split rear end. It was a powerful truck.
Also I had a 400 international with a 4 speed and split rear end it would do 80 mph pulling a trailer with a heavy backhoe all day long.
Would any of these giant torque monsters be good candidates?