Moving the wheel outward towards the wheel lip, generally works a bit better than the reverse. If you think about what is happening to the body and suspension when cornering, moving the wheel out doesn't post as big of a problem as moving the wheel in. Imagine you are turning hard left. The body on the car will tend to want to move out and away from the outboard wheel of the turn, while also pivoting downward. Although the body is getting closer to the wheel on the inboard side of the turn, the body is also pivoting up and away from the tire.
There is a point where it's too much though, you do still have to have some space between the tire and the wheel well lip. But in your case, the move from a 5.5" BS to a 5.3" BS shouldn't be an issue.
On an 18" wheel, a 27" tall tire will have around a 4.5" sidewall. Compared to the 29" tall combo that will have around a 5.5" tall sidewall. Honestly if you want 5.5" of sidewall, I wouldn't be looking at 18" wheels anyway. I'd put a 15" wheel on there. You're getting the same sidewall size by doing that, and you're in a 26" tall sizing which the car was more designed to handle. As b-man has already shown, increasing the tire height starts to require modifications to the wheel houses, or you need to jack the rear end up in the air to add clearance.
A 28" tall tire would split the gap here and give you about a 5" sidewall. That would be a 255/50/18 size.
I've included a pic of my wife's previous Chevelle. This is an 18" wheel with a 27" tall tire; 275/40/18. Everyone's taste is different, but I felt like this was still a good amount of tire.
