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Sure. When you go around a curve, the car has a natural tendency to lean out, as though you would fall over. The bar uses downforce on the outside wheel to create upforce on the inside wheel, keeping the car more flat in the turn. A thicker bar increases the ability to do so.
I put a 1" on my 64.5 and I really like it. Really cuts down on body roll and the ride is not noticeably harsher. The 1" was supposed to be temporarily on 64.5 until 67 painted. Now I am torn because I like it so much on the 64.5. My 67 does not roll much because it has higher spring rates.
Unless you have something specific in mind, just get the stock GT springs, and something like KYB GR2 shocks. I use the Gas-A-Just, but some find them too stiff. I removed a set of Konis when I installed them, so they feel pretty soft to me.