OK, Let's start from scratch here....what brand and model servos do you have on the Elevators? If you have HiTech digitals you can reprogram with a Hitec servo Programmer. If Not then you will probably need to buy a "matchbox" or similar device. OR buy servos that can be programmed, OR buy a radio that can do the job.

If you have digital HiTech servos you can maybe barrow a programmer to set them up for you. Lots of Hobby shops will have these available to help with this very thing. You may not have to buy one.

A reversing Y Harness will NOT allow you to match the surfaces without using some other devise with it. So that's not a good solution.

Sorry to tell you, this ain't a cheap plane to set up. It's a bargin to buy but can get real pricy to get set up if you don't have the radio for the job.