Was searching for a 3.73 9.75 axle today and came across a 7 lug axle in a F150 for sale.

My question is can one simply swap the 6 lug axle shaft into the 7 lug axle housing? My truck is a 2010 and the axle is from a 2011.

I'm also not sure why the 2008 axles seem to be cheaper. Is there a reason to not buy an 08 or older 9.75 and use it?