I would go for the larger wheels, check out the Camaro that we are building now with 19X12.5 on the rear.
http://www.feslerproductions.com/1969FeslerCamaro.htm, it is worth the extra work to get the larger wheels on there and if you have any questions on how we did it email me. I have two 69Camaros right now with this size in the back and they look sick.
Chris