VFD is the way to go, you can get them for just about any motor, 1~,2~ or 3~. If starting from scratch have you seen this?

opensourcemachine.org/.../2008/10/how_to_build_a_multimachine1.pdf

For some reason I cannot upload files! This is a very good example of 're-purposing' and has led to using old engine blocks as the base for all sorts of machinery.