For towing and hauling you need torque, not horsepower..... Rather then spend a bunch on your small block, the easiest and probably biggest gain for the $$$$$ would be to replace the SBC with a Big Block Chevy..... A stock 454 will put out more torque then a much modified small block built with torque as a goal, and it will do it at a lower RPM which will also increase the reliability.....