I would try to let the tractor get to full operating temp before you drain the hyd oil, if possible.
the last time I change out the hyd/trans oil in my old 1957 TO-35. i put the plows on and broke up a few garden spots then disc them down.
by the time I opened up the sump drains the oil was up to operating temp. You will get much more of the evil dirty stuff to drain out, if its hot,
note to file: it may take a full day for the oil to drain out. do not be in a hurry, let it drain until it stops running out. tractor has been setting for 8 years another day should not be a problem.
reason for this procedure, 8 gals of NAPA, GL-1 oil is not cheap, so you do not want to have to do it again.
that would be what I would do: if nothing else just hook to a log and pull it around until the trans oil is hot, work the lift a number of times to cycle the oil.
be sure the lift is in the down position when you drain the oil so most all the oil is out of the lift piston cylinder.
if you had only known, before you moved the tractor you should have cracked the trans drain plugs and let the water drain out of the sump, sometimes you can get up to a cup full of water out.
after the tractor sets for a week or two one should crack the trans drain plug, from time to time, and let any water drain out. the water will collect in the bottom.
as I understand this is where the pump pickup is located, so getting the water out is very important.
if you drive the tractor all the time the water stays mixed so it will not freeze and bust parts!!!!!
but get it out is best and change the oil.