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.
it looks like you are going to have to pay the $107
http://www.amazon.com/Microwave-Transit ... 0890062358
Have you tried contacting the author? Maybe
he'd be willing to help you with your project.