I made a new rig last year using the same principle.
I used 3/4" galv pipe with a bit of pine fixed to it for the neck pocket. It works a treat.
I clamp mine onto my 20 y/o B&D Workmate portable bench.
I hope that chair is heavy enough to counter the body weight. I'd hate to see a post about a freshly painted body crashing to the ground!

Click image for larger version. 

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