Ryanlesser, Is sounds very possible that the person who modded your model 16 to 16.5 status made errors in assembly-installation?
I wish to help, with a list of measurements from a genuine VPI 16.5, and let's see how they compare? I should note, VPI should as well be able to provide, and confirm these simple measurements, particularly, what the Pivot-Spindle distance is on a 16.5 RCM.
Firstly, the inside width of my 16.5 from left to right inner wall is exactly 14.5".
The center of Spindle to center of Vacuum Tower Pivot is exactly 7-1/16".
The right side of vaccum tower bezel edge, to the right inner wall of my machine is exactly 1/4". (ample clearance that the bezel does not rub the right inner wall)
With Record mounted on my Platter, which is a custom acrylic platter, but exactly the same dimensions as the original 16.5 platter, the record's left edge is exactly 7/16" away from the left inner wall, and 2-3/16" away from the right inner wall of the machine.
I think what ever way you approach it, the Spindle to Vacuum Wand Pivot distance will be what's important, and will be largely dependent upon how wide the inside of machine is, to be able to re-mount the Motor Mounting Plate further to the left? (without the record now rubbing the left inner wall of the machine?)
It may mean slightly enlarging the hole for the Motor, with either a dremel tool, a sabre saw, or roto zip tool in order to slightly shift the entire Motor itself to the left, slightly away from the Vacuum Wand Tower? One could simply epoxy-bondo the existing mounting holes for Motor Mounting Plate, and start over.
Hope this helps, Mark