d26 ...........Thats not trans oil you drained my friend it is shuttle oil ........the trans oil is a shared compartment with the rear end oil and it is a 80-90wt oil in there ...........the shuttle is the hy trans oil like jusk said and the best stuff to get for it is the case brand tch they do act a little better with the case oil rather than the tsc stuff.........
In this pic is the dipsticks for the shuttle compartment its the one in front of the shifter and the one behind the shifter is for the rearend and trans......they are about a 1 1/8 socket to remove them and theres a dipstick attached to them ...........
Under the tractor is 3 drain plugs the one you removed which is all the way forward under the bellhousing then there should be one about half way back these 2 are for the shuttle compartment i drain both when i change shuttle oil............then there should be one back further for the trans/rearend oil (80-90)...........
Im pretty sure jusk is also right about the 17 qts for the shuttle and im thinking about the same for the rearend/trans oil .....seems like 1 -5 gallon bucket of each does the job with a little left over...........
dont forget there is a shuttle oil filter in front of the radiator you should change while your changing the shuttle oil..........
If you need anything else just let us know..........