Some of you may have checked this guy out but he does have a 4 wheel set up for an EZGO for a little over $700.00. You do have to send him your front spindles so he can weld the mounting brackets on. He used a jig set up so the bracket is lined up just right. He does not charge anything extra for the mounting of the brackets, you would just have to pay for shipping. Here is the link to his site.
http://www.sanclementegolfcarts.com/
Jimbo