The problem was partly caused because the original legs were at full extension. The replacement legs were longer than the originals and were more secure at the needed length.
One difficulty was that the threaded base plate where the legs screwed in had been damaged and had to be reshaped, I was able to reshape the sockets with some effort, to allow the legs to thread in, though one remained slightly angled. (A metal tool of some type which could be threaded in and used to bend the socket area to the correct angle would be useful; the plastic legs aren't strong enough to do bending of the bottom plate.) Had to raise the range up on blocks to be able to work on the bottom plate sockets. Replacing the legs was easy, fixing the sockets for them was challenging!