Power is subjective and dependent on RPM. Torque is actual and measured. The higher the low-end torque, the taller a frame you need to resist twist.
One thing that I have seen is stacked frames on a few trucks. Two 3/4T frames stacked on each other with minor modification
I agree, an original 1 or 1.5T frame would be sufficient for your needs however dependant on the suspension geometry and design that you will be running.
Like Oldsub and Grigg mentioned. Plan the truck first. Class, Rules, weight, power requirements, engine location, tires, wheels, axles, gear ratios, suspension, steering, fuel tank location, weight transfer, CG location, suspension adjustments, etc. once that is done, sketch out how that all fits together. Then draw in where the cab is going to go. After that, determine if a stock frame will work as is, with minor modification, or do you need to start from scratch.
You may find it easier to start with a clean sheet and build the frame that you need. I have helped design many rectangular tube frames for mud-running and rock crawling vehicles for friends who play in the mud and roll-over test their vehicles. Usually 3/16" walled 2 x 6 (Jeeps) or 2 x 8 (Trucks) tubing with 2 x 6 or 2 x 4 cross-members is what I used with the 4-link being tied to 1/2" plate that also mounts the transfer case. Skid Plates were made out of 1/4" plate with reinforcement and mounted to the cross members to protect the oil pan, transmission, and transfer case. Driveshafts were retained in cages
Scott
