check the timing
radiator may be stopped up on the outside and not letting air flow through the radiator.
remember a radiator can be stopped up on the inside and it can also be stopped up on the outside not letting air flow through the radiator cooling the fluid.
i know the older tractors do boil gas, but i have a t0-35 and it never has boiled fuel. I just do not want the the motor hot enough to boil the fuel when i am driving the tractor.
lack of oil pressure is the fastest way to ruin the old motor, the second fastest way to ruin the old motor is letting the engine get hot.
have you washed the radiator out backwards with a water hose insuring the fends are clean. Is the fan belt in good repair and not slipping, may only be turning the fan at half speed.