Okay, this is done now and I thought to give a review how it worked best.
Somewhere above is the hint of using a 1 1/4" forstner bit. This is too small. Even a 1 1/2" forstner is still not large enough, 1 5/8" or 1 9/16" would have been the right size. Non available at my local hardware shop.
The washers are stainless, so I sanded them on the belt sander to fit. I sanded the edges and inside of the counter sunk recess and triple applied urethane clear paint before installing the washer with the 3/8" SS carriage bolt. The washer can be turned in the recess, I used a fitting easy-out that one uses to remove broken-off bolts, since the tool is tapered, it can be easily set inside the washers 'star-shaped' hole to turn it.
Picture to follow.
The process was actually quickly done for the six holes. Just take your time for the actual drilling of the hole so you don't drill too deep!
