I myself went the old standard MK-IV Platter with my bought new in '96 JR Table. (Standard JR MDF Plinth w/Sorbothane Pucks)
The Changeout was no effort, as the older MK=IV Bearing Well dropped right in.
It was then as others have said, getting all other paramaters adjusted. The extra weight, which fortunately is evenly distributed across the Plinth did cause a slight drop in Plinth height, and also due to the elimination of four spindle washers that VPI themselves placed, placing one washer upon each Sorbothane Puck.
This was no doubt done by VPI to insure clearance between the Motor Pulley Cover, and Motor Pulley.
Once I installed the Heavier Platter, and removed the Spindle Washers, a clearance problem occurred between Pulley, and Cover, and a slightly thicker rubber washer was then needed in betwen the three standoffs, and cover.
The other issues may be also Dustcover clearance between it, and the Spindle Clamp. I had this problem, and let a good freind fabricate a beautiful solid Billet Aluminum Screw Clamp Puck, and I'm utilizing an older BDR Coaster in combination with it (two piece clamp).
Lastly, when the MK-IV Platter was installed, naturally VTA needed to be raised, and with my own AQ PT-8 Arm, there was a heck of a lot of Tonearm Mounting Shaft showing on the arm, and it looked horrible.
Here again, for a small price, I opted to let my freind machine a .5" thick Aluminum Spacer (Donut) and installed it between my Arm, and Plinth. Since the Original Tonearm Mounting base was still used in this configuration, there was no need to install a means of retaining the Arm with the spacer (Allen Locking Screw)
Other options, yet more costly, to aleveiate-correct this issue, would've been perhaps the Pete Riggle VTAF device, and this would've increased Arm height by I understand .250".
The other feature gained by this device is the ability to play with VTA settings on the fly, an option I don't have with the .5" Spacer, and felt I didn't really need.
Not long ago, I did see VPI still state they had remaining stock of Mk-IV Platters, and cost was listed at $700. I assume this Platter uses, and came with the newer, inverted Bearing.
Hope this helps, Mark