Change oil after the first 350 miles and then every 12000 miles.
"It is recommended to remove the transmission oil when warm by using an automatic oil suction machine with the tube end inserted into the vent hole."
If an automatic oil suction pump is not available, remove both "a" drain plugs as shown.
This operation is rather difficult, and the drained oil can spill into the bilge, requiring draining through the bilge drainplug hole, or cleaned out in other ways.
What a mess. Thanks to John Freise for his kind donation of an electric suction pump! Hope it has the power to pull that viscosity!%
Kirk: More Power Scotty!
Mr Scott: Im giving it all shes GOT, captain!
Re-fill with 4.4. pints of oil SAE 90.