$20 worth of scrap 8mm aluminium plate, some stainless bolts and countersunk screws from below. You do need a recess in your pier top plate for the centre bolt and a very solid 12mm overhanging pier cap plate on 80 mm solid bar. (If you wish to bolt from below but I suppose you could tap the plate.)
Cutting a 60mm hole in the plates is the fun part.
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