After a little searching I found a couple pictures that show where the rear dowel pin is located on the torque tube.
And I believe the dowel pins are on the underside of the torque tube facing the ground.
Pic 1 Pic 2 The rear dowel pin is located pretty far down the narrow portion of the torque tube.
The u-joint ball housing does not reach that far down.
There would be no interference with the retainer rubber oil seal.
You could leave it open or slide a wood dowel down the torque tube and weld up the hole.
When done pull out the wood dowel and grind smooth the weld.
Pic 3
