Thank you Sunny. I dont post much but this is something I thought I could help with.
Some further thoughts/tips because not everyone has access to tools.
You can go to a Lowes, Home Depot, Menards etc and buy 1/2" or 3/4" plywood sheets. Then get them to cut it to your shelf size. Have them cut (3) shelves for you say...24"x18" each or whatever your self size needs to be.
Then, if you dont have a drll press or forstner bits to drill the large diameter "recessed" holes to fit over your nut/washer buy a hole saw (of the dianeter thate you need). Drill the (4) holes using your drill or have a buddy do that for you on (2) of the (3) shelf pieces. The hole saw will cut all the way through it. Then glue those two together carefully lining up the holes.
Now glue the third shelf (which has no holes) on top and you end up with a solid top with recessed holes underneath that doesnt require high end tools. Presto!
Last tip: ( sorry for the long post)
If possible unbolt your existing top shelf and use that to line up the holes on the new shelf you are creating. That way you wont need to guess where They are nor make high precision measurements.
Lastly, once you have the position of your holes, take one of the washers and trace it in place so now you know "where" the holes go and"what" minimum diameter you hole needs to be. I recommend making your hole slightly larger.
If you want to get fancy you can use different materials for that top shelf to create a multilayer turntable shelf that would isolate different frequency of vibrations depending on the materals (mdf, plywood, corian etc) used in your shelf.
Hope it will works for your. Your choices are only lmited by your creativity.