I've been told the rule of thumb on inline 71s is 35 HP and 100 FP torque per hole, that would be 140 HP and 400 FP. My book only lists 6-71s and 6V-71s, the 6-71s range from 201/552 to 260/751. I would think the 4-71s would come in several different ratings also.
Jared