Given the body diameter, taper, and length of the 6.5-284 can a barrel with a 2.5" shank (Lilja Medium Palma) be set back and rechambered to 6.5 Creedmoor, 6.5x47 Lapua, or .260 Rem when fitted to a Remington 700?

The 284 case shoulder dia is .475" Everything else you have listed is around .473 at the base. So you would have to see the barrel back the full body distance of the 284. Or 1.758".

So If my mind is working. Start with a 2.5" shank. Cut 1.758" off leaves .742" Thread length shank for the 700 is .885"?

Seems like a mess to me.

Guess it's time for a new barrel.

UNLESS there is 2.5" of shank PLUS the threaded tenon. Then there's plenty of room!