Have a problem need some advice.
 

So I removed my head only to find the pistons leaving metal residue in the cylinders. My buddy is an engine guy and he says that the pistons looked as if they had started to melt and were leaving traces on the cylinder walls of 3,4 and 5. So now Im trying to figure out what I should do. Should I go with the JDM and just drop it in or should i rebuild this one? JDM roughly 1000$ or rebuild- price unkown. has anybody had any luck with JDM's? Or should I just buy a rebuilt 7MGTE if so does anyone know of a good place to get one?

All responses are greatly appreciated.

Used is used... I would NOT just drop in any used engine. You have no idea how long it's sat outdoors on a rack in a yard, how it was driven or how well it was cared for. If you want it to last plan on rebuilding any engine you drop in.

If temps were high enough to cause the level of damage you're talking about your block and head may have warped beyond serviceability. Look up the specs in the TSRM and measure them.

Sounds like you maybe running lean on those cylinders. There are a ton of components that could be causing it. Injectors, bad/missing EGR, fuel pressure, fuel pump, fuel filter, etc. The 7M is a strong motor and when treated well it's a bullet proof motor. A stock bottom end is good for 450-550hp. 1JZs are cool but it's, in my option, too much money for the swap, then you have to put ALOT more into to get HP gains. Rebuild your motor, check and see why it's going lean, and use the money you save towards a few HP adders on the 7M