I too had to add a headshell wieght to my JMW 9 on my Scoutmaster. I installed it on top of the headshell. Although it doesn't look the greatest, it didn't require that I screw around with tone arm height. I did have to re-check alignment, azimyth, and VTA (I have mine set at the high end of what VPI recommends). All turned out successful for me. I hope it does for you too.
Good luck!
Good luck!