Here's an old old thread that's got a few posts of one of my Edge540's that I installed rear-mounted servos... if you look at the thread.. just scroll down about half-way to my pics/text... it lays it out decently.
As for the one servo needing to be reversed... I got a "servo-reversing Y-harnes" It was $9.00 at Horizon... these have a potentiometer so you can match throws exact..servo to servo.
The date on the thread is Nov.'02... the plane, servos, all of it are still going strong..matter of fact I'm flying it again this weekend. Check it out.. this does work well, and is easy and affordable.

http://www.rcuniverse.com/forum/tm.asp?m=359864