Yes, with the Garrard I built a baltic birch plinth with multiple layers anticipating big performance gains, but the performance was mediocre at best and very disappointing. It was a reasonably substantial plinth, but not until the Porter and Semrod designed panzerholst plinth did I realize the potential of the 301 turntable as a reference turntable. Their massive plints with numerous tweaks to enhance the resolution elevated this idler wheel turntable past some very formidable competition.
I am also using the Loricraft motor controller with the torque control, which recreates the original 50 Hz sine wave that the 301 was engineered for in the 1950s (courtesy Steve Dobbins). Presumably this improves the operating smoothness of the powerful 301 motor to reduce rumble and noise. The torque control allows you to reduce the torque and still maintain speed control with the net effect further reduction in vibrations.
The Technics Mk II arrived in their top of the line Obsidian base, which was not to bad, but certainly not in the same league as the Porter panzerholst bases. Transformation is amazing and moves these turntables
to the top levels of performance.
My mark III arrived with no base for any comparison.