RB300 VTA adjustment on Nottingham Horizon

I recently purchased a Nottingham Horizon and an RB300 from separete sellers and am now trying to set VTA on the arm after installation - how in the heck is this accomplished?

The screw-threads on the base of the arm will not extend far enough down.

Has anyone out there experiecned this?

I've got a virtually new setup that I can't use - this stinks!

Any assistance is way welcomed!

Thanks,
Mark