Weight, Clamp or stabilizer?


I have a vintage Pioneer PL-560 Direct-Drive Automatic Turntable purchased around 1980. 
https://www.vinylengine.com/library/pioneer/pl-560.shtml
I'm trying to get it to produce the best sound its capable of.  I plan to order a set of SVS subwoofer feet to replace the worn feet (I have an SVS subwoofer and removed its feet and temporarily placed them on the TT base with good results).  I read an article about TT tweaks.  A few things they suggested were an upgraded mat, clamp and isolation feet.  Thing is since the TT is a direct drive I don't know how much extra weight it can take (if any), and the spindle is about 7/8 inches tall so I don't know if that's enough for a clamp.  The original rubber mat it came with is in great shape. Do I need to replace it, too? I'm willing to invest in tweaks to improve this turntable, but not interested in replacing it.
mewsickbuff
I have the Shure m97xe high-performance magnetic phono cartridge. The arm is the original arm. I found instructions for cartridge and my specific turntable's arm setup online in the operating instruction manual, rare and detailed.
I did a lot of research in the form of reading shoot-out review's and forum lurking over the mat and record weight upgrade for my technics direct drive table and ended up with a 5mm funk firm achromat and an oyaide stb-msx record weight. Both have made a significant improvement to my table and I'm quite happy with the results and don't feel I need to upgrade anything. If I remember correctly, for steel platters, using a record weight is more effective than a clamp. If the platter is made of glass or acrylic (rega or project) using a clamp is more effective as it doesn't add unnecessary weight which may cause smearing.

This is of course based on the findings of others that have tried it and not my first-hand experience. In my case, the achromat provided a bigger 'upgrade' compared to using the stock technics rubber mat. The oyaide record weight was a more subtle change, but a pleasant one and it looks great and makes my table look the business.   


Regarding turntable feet that are adjustable, there are two fairly-new excellent ones: the IsoAcoustics GAIA (reviewed by Art Dudley in the June Stereophile), and the Townshend Audio Seismic Pods (or the company’s Seismic Platform, which has Pods attached to it’s bottom.).
chakster....Thanks for your recommendation. From what I've found, the AT-616 isolation feet are no longer in production. There are some sites that list used ones of a price from $600 to $800. More than double the cost of my table and cartridge.

So....Would the cost of the feet really be worth it given my setup? If I had a more costly table and cartridge then, maybe. I realize that setup is most important for any table. I am looking for a modest tweek that may or may not yield any sonic improvement. Certainly not high dollar feet meant for more exotic setups. Thanks anyway for your input.

A set of four IsoAcoustics GAIA III (which support up to 70 lbs.) retails for $199, $189 on Amazon.