The pressure would depend on the RPMs although I'm not sure what the stated pressure is supposed to be. Another thing to keep in mind, is that any system you find will be 30-40 years old. Wear and tear must be taken into consideration.
As for weight, a good working unit will lift and hold any attachment. The heaviest are the flail mower, tiller, and snowcaster.
Use 30w non-detergent oil in warmer weather and 10w in winter. Check hoses for cracks. Even a weak system will soak tractor and operator.