I would think adding a trans brake to his trans will shock the tires so much it will not hook either, requireing different launching techniques also.
He has no traction bars or caltracs.A trans w/a lower first gear will be a bit more controlable as compared to using a trans brake.
Trans brakes are so vilolent it feels like your car gets rear ending everytime when you let go of the trans brake button.

I do not think it will net him 3-4 tenths right off the bat & not changing anything else IMO.
I think in comparing your monkey truck that hooks up dead nuts no matter what you did to it, big tire/slicks, as to his 24" short tires @ 3052 lb car. Not a good comparision IMO.
HMMM, lets see,,, he brakes the tires loose @ 3000 RPM,,(currently he looses traction @ 3000 RPM) add a trans brake so it will stall another 300-500 RPM , so potential launch RPM would be 3300-3500 RPM, same 24" tires, no traction devices.
You are correct about the 3-4 tenths, but it would be in the other direction 3-4 tenths slower LOL.

Also, IMO, comparing full blown race cars to his car & giving him examples of what race cars use really does not help his cause.
Sorry, to me adding just a transbrake does not make sense, so I had to say something,,, maybe I'm wrong?
Just my two cents, take it for what that's worth.
MBHD