Why you did that ? You could just add Micro Seiki CU-500 gunmetal mat on top (perfectly matched). Here is mine. The weight of CU-500 is 2.7kg and it's 5mm thickness. That was huge upgrade for my stock SP-10 mkII.
When you're using not original parts, but some overkill superheavy custom platter why do you expect improvement ? Technics platter is already heavy.
Then why are you adding mass to the platter also? It is already designed to operate as the engineers at Technics intend it to, yet you feel you can improve upon that.
This is no different than what I originally did, which followed the line of thought of increased platter mass would improve sound quality by less resonance and increased rotational stability. For me that was not the case, and I returned the item and gained a bit of knowledge/experience of what I prefer in turntable configurations.
I am noticing something about you. It appears you are one of these people who believe that your choices are the only correct way to do things in this hobby. If others disagree with you or have a different perspective then they are misguided or ignorant. Audio is a journey and there are many pathways to take, and folks often have a different destination in mind and value a different perspective of what they get to hear and experience. Honestly, it would make my time here more enjoyable if you would refrain from interacting with me. Unfortunately this place does not have an ignore button.