What is wrong with your motor that you think you need a full rebuild kit? I thought you were having overheating issues that you thought might be related to the cylinder head?
My recommendation, is leave the bottom end of the motor alone. Check the compression, and if it's good just rebuild the cylinder head only (assuming cracked cylinder head is your problem). I've seen soooo many Toyota diesel rebuilds not only cost a fortune, but fail shortly after. Mud is full of these stories. So my advise is: "if it ain't broke, don't fix it"
A new cylinder head can be done in about 10 hours. Set aside a weekend and take some extra time to clean the intake manifold, paint some parts etc.
All that said, I have bought some stuff from that Mag Engines seller before with good success. Those particular pistons shown above don't seem to have reinforced piston ring lands. That is one thing that would concern me. The factory 2LTE pistons have ceramic fiber reinforced alloy ring lands and are tough as hell.