Why wouldn't you rebuild the one you have?
Then you know what you got.
Rebuild engines have shipping(engines weigh a bit, lol) and warranty does not cover labor and usually only covers shipping it one-way.
So I would ask mechanic what he would do, i.e. pull the head and block out of the truck
And then send BOTH out to a local machine shop to be rebuilt
Then mechanic reassembles after its done
All local, all warrantied locally
Can't be without a vehicle........thats why we have friends,

, and you can always rent a car for a week or two as part of the cost.
Rock Auto lists 2.5l Lima long block for $1,600 + $300 core deposit
Long block is rebuilt block and head bolted together ready to install, so just add other bolt on parts, i.e. oil pan, valve cover, water pump, ect...
Master rebuild kit is usually about $500-$600
So if local machine shop comes in at under $700 labor then you are saving money PLUS no shipping cost