I wouldnt mess with the time effort and money, 3.6's sell like hotcakes on agon. Flip yours for the finish you desire...even at a loss I cant imagine the cost exceding changing the trim on your esxisting speakers.
Your best bet is to call Magnepan. They will provide you with new rails and installation instructions. They are very, very good with customer service too!
You must have a verified phone number and physical address in order to post in the Audiogon Forums. Please return to Audiogon.com and complete this step. If you have any questions please contact Support.