back up planI looked up the torque rating of that coupler,. Roughly 3600 in-lb = 300 lb-ft.
The problem I see is your shaft is splined not smooth so you will have a greatly reduced clamping area. Lets say 20% = 60 lb-ft and easy to erode if it slips. I am also not a fan of those spiders in applications like this.
What happened to the custom bolt on hub idea?
Dan