The 06 is a bit longer so my guess would be the barrel chamber would have to be shortened, rethreaded and rereamed (or buy a custom barrel and build from the ground up). Probably way more effort than it's worth. I'd just sell the 03 and buy myself a nice .308.. Even if you got the 308 to chamber you'd still have a short cartridge in a long action and I doubt it would ever feel right.
2004 Astro AWD 3:73, G80 "locker", 2" lift, overnight-able, "E" All-Terrains
2003 Dodge/Cummins quad cab 2wd
2006 Nissan X-Terra 6-speed (for sale)
1985 LTD LX 5.0 HO project
+ wife's and kid's cars