This theoretical solution of copper saws and abrasive have been debunked. While proven possible given the location of many saw cuts, copper saws are just considered not feasible.
In the numerous saw cut examples and especially in the quarries, there are large radiused circular saw marks in the stones. Some sort of circular saw was apparently used. There are lots and lots of the circular saw marks
The point was that as I started writing that post I remembered my #8 Jointer Plane (heavy critter, but very satisfying to use) and thought why not place a soft shoe on a heavy wooden block (got some of those old planes too) and use it to push around grit to smooth and true stone surfaces?
Then, having pondered that I recalled my moulding plane which, or rather an ever finer series of which, could present a solution for fine radius corners.
These, discounting providing the flow of grit slurry, would be mechanically simple tools but might work to produce the desired results.