placement of quad 57's

Agree with Whart, you will have to experiment. I have mine about 5' from the front wall (to the center of the speaker) and a little under 2' from the side walls. I sit 8' from the plane of the speaker and they are angled so the tweeters are aimed directly at my listening position. I have not had these for too long and I am still experimenting with position and damping on the front wall. I have mine on stands and mounted 14" off the floor. This is my last pair of speakers - everything else I have owned (lots over the last 30+ years) pale in comparison.

You will have to experiment. Out from the back wall, probably more than you'd think, toe-in varies depending on distance to listening position- height off floor makes a difference in balance; on the original legs, you might also consider what the floor material around the speaker is made of; make sure you have a pair that is in good condition, and has been gone over by a reliable source. They make music like almost no other speaker, and spoil you on coherent midrange, despite all of their obvious limitations. I have a pair moldering in the basement which are in desparate need of restoration- someday I will get to that.
I also have a wonderful story about how the girl who became my wife established her bona fides early on as a result of my Quads. I'll save that for another time. (No, it is not lewd).