Platter upgrade for VPI MkIV?

Yes, of course.  But the bearing that does most of (indeed, almost all of) the turning is the non-inverted bearing.  My only point was that there is a popular misconception that inverted bearings are inherently superior and non-inverted bearings are inferior.  The excellent performance of the Avenger Reference proves otherwise.   The inverted bearing isolates the slave platter from speed variations of the drive platter, but not from its non-inverted bearing.

As stated, a major advantage of a non-inverted bearing is that it sits in an oil bath.

.....and the major advantage of an inverted bearing is that the majority of the mass is below the bearing / thrust pad's center of gravity. 

I do however, agree with your statement that both inverted and non inverted bearings have advantages and disadvantage and what matters most is the quality of the bearing.

BTW, VPI never made platters with a combination of acrylic / lead or metal, they used Delrin / Acetal.  VPI did for a short period of time made platters out of  both 100%  (frosted) acrylic and carbon infused (Black Knight) 100% acrylic, which by all accounts (including me) were the poorest performing. 

The stainless steel TNT Mk5 bearing with the rulon bushing and heavy stainless steel retaining donut is as good as it gets.  If you have not done already, I would suggest replacing the 0.25" ball bearing with a ceramic silicon nitride (Si3N4) grade 3 ball bearing.  Also, if you have an extra thrust pad, have a local machine shop drill out the tungsten pad and replace it with a thrust pad made from PEEK. 

Thanks for the bearing tip.  It's on its way.  About the thrust plate, I'm not so sure.  Do you think VPI may have an extra thrust plate?

It may be that you are correct about the Delrin, but I think we and VPI have been using the term "acrylic" for a long time, even if incorrectly.  I know that HW has written of the " acrylic lead combo".  Also I Googled "VPI Super Platter" and came up with some VPI promotional material which reads in part, " Made from an acrylic/stainless/acrylic sandwich (just like the HRX chassis) and weighing in at 25Lbs this is a big bad platter upgrade . . ."

But more importantly, thank you for your contributions here and on the VPI site.

I like the TNT MK III platter best, of all the VPI platters.

Cork, lead, aluminum, with acrylic top layer.  Oil well bearing, machined to perfection, that lasts forever.  No tilt or run out, spins true.  Simple, effective.

Indented center, with washer, for use with screw down clamp. Pushes record flat without dishing.

Acrylic tops mate better with vinyl, which is acrylic.

Balanced to perfection.  They made about 100 per year.

Cost $600 in the late 90's.  Would cost a fortune to make today.

Better than the later Super Platter IMO. The Super Platter could not be manufactured without problems.

I do not like metal on the top, because you can not see if the dust is cleaned off.

I upgraded my Mark II with a Mark V platter and bearing. The bearing upgrade required drilling bearing opening but found a precision machinist to do the job. I replaced the stock springs with Herbie's feet and got the correct height.

You can see the project progression here vpiindustries.com/forum/viewtopic.php?f=9&t=140&p=1136&hilit=austinbob#p1136

I'm pleased with the upgrade. Still haven't bought a SAMA but still plan to do so.