With the hubs you’re going to be somewhat limited. Pad on top would be an interesting experiment. I had the raptor 1 which vibrated like crazy, I did Abec 11 wheels and softer risers, but adding all that together AND riding in running shoes finally made it tolerable on less than perfect roads.
I’m on the waiting list for the X thing, but can’t seem to find simple mounting plate. I though it would be pretty common for topmounting on drop through decks.
You’re right just the washers could work as well. I’ll need to try that. But, I think it will cause a bit more slop compared to using a plate or the X thing. I’m thinking about cutting up a shock pad.