JLJ,
That question was just discussed over on the H. Ferguson forum.My 1957 TO-35 has the orginal oil guage on it, all it says is (low, normal, high) so I do not know what oil pressure to tell you that mine runs. Their discussion level out after numerous inputs that the oil pressure should be between 20-35 psi. So who know what is should be. Be sure that your oil filter canister still has the spring in it. This spring pushes the oil filter down against the block, forcing the oil to go through the filter. If spring is missing, then oil just circulates around and is not filtered. Many springs are dumped out with the old filter and if you are not aware that it is suspose to be there you will just replace filter and be on your way. Are you running a straight 30 weight oil or 10w40 etc: If tractor is running good I would just go plow or bushhog and not worry with it. I like to use a qt of Lucas Oil Stablizer in older machines, seams to me that it keeps the motors a little quieter. Many big semi truck owners would not let you change oil in their trucks without adding Lucas.
So if its good enough for them, then its good enough for a little Fergy.
I also use a qt in the transmission. Good luck and stay safe.
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