Usually you adjust both to get a balance.
all Toro workshop manuals are on the Toro web site .
You can never get the lap bars even on mowers with indiividual pumps.
On the older ones with a single pump that feeds both motors you can get them balanced but again it is not easy to do and will vary as the temperature of the motors changes.
Usually the left side drives on Toros gets a lot dirtier than the right so it gets hotter, the oil thins more & the drive looses power.
If you search through the archives you will see that it is usually the left drive that fails first.