I not only put brakes on my swivel table dolly but also widened it to accommodate a full size vehicle.
Would I do it again, yes but only for the breaking advantage.
I would have bought a dolly that was wide enough but the braking is a have to as pulling 4500 lbs. causes a lot of force of motion when you have to break hard.
I got a garage to install the surge brakes. The cost to install was about $500.
finally, would I do it again, NO as I now own a dolly that weighs over 800 lbs. and cost near unto $6000. It is cheaper to buy a good dolly with disc brakes and forget all the hassel with retrofitting brake assemblies.
Hope this what you are looking for and Good Luck on your choice.