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 don't think most decent turntable bearings care much about a few ounce or a pound weight or clamp on it.  I mean a VPI Prime platter weighs 20 lbs and as you know many platters weigh a lot more.  I suspect the bearing can handle a weight just fine.
For a platter mat, you could look into the Herbies Way Excellent mat. 
They’re made extremely well and can be ordered for any turntable. I’ve had mine for a few yrs now, and I really dig it. 
You could also check out an Achromat, which are very high quality as well. 
I posted before, that I put a stillpoints clamp on my Avid Acutus Dark, and no longer do so. This is because the clamp made the sound somewhat duller ... lost its musicality and airiness. In my system is a waste of £400