Early belly pumps were rated 500 psi, later in productiion tolerances were improved and were rated 850 psi. Rebuilds after that time also improved early pumps to 850 psi.
If you have the same fluid, #303 in the cylinder on the rake and the H, park the tractor close to the rake and hook the hoses up and try it! Remember, cold fluid is "thicker", more viscous, hot fluid is thinner, tractor won't lift as much with hot fluid as it will with cool fluid.
A larger diameter cylinder will make up for the low psi. Going from a 3x8 cylinder to a 4x8 cylinder increases lift capacity by over 77%.