Dude, I looked through the IEEE publications (my company has a subscription), and there is nothing there for you in terms of equations. There are about a dozen papers with microstrip to stripline transitions but they only present the results of the works, and cite references like the "Microwave Transition Design" by Izadian that you mention.
Unfortunately it looks like you are going to have to pay the $107 from Amazon.http://www.amazon.com/Microwave-Transit ... 0890062358
Have you tried contacting the author? Maybe he'd be willing to help you with your project.