@rsusuki, it is a beautiful & mature design.
Since the design looks So complete. It’s difficult to add or modify something to attend the joinery requirement.
I will settle for 170lbs…if it is OK.
Some options…
- Add a metal sheet as a stopper.
- Go for the square hole (or non circular shape) and sq. rods attaching them.
Here are few quick googles…
Square Hole Broach
Mortise Chisle