'06 Impala - how to change spark plugs + gap spec.

I'm planning on replacing my spark plugs in my '06 Impala 3.5L 6-cylinder. The three front plugs are easy to get to, while the back 3 are going to be difficult to get to. I've heard of people having to rotate the engine forwards to get access to the rear. Is there any way of avoiding this on the Impala? If not, what are the steps to complete this?

Also, what is the proper gap for my vehicle? I've read online 0.060" for my engine, while the bigger impala engines are 0.040". I pulled one of my plugs out and it measured at 0.040". Is this correct, or were they not properly gapped last time (if ever) they were changed.

Thanks!