skip.to.maloo

Hi guys, I am currently stuck between a rock and a hard place. I have a 2002 Subaru Liberty/Legacy with a 2.5L N/A engine and auto trans. I know the short block is a dud and the heads was recently reconditioned. I have exhausted all other options and have 1 option remaining which is to replace the engine. I have been trying to find a low kilometer EJ25 Gen3 but deemed unsuccessful. However there are heaps of Gen5 and several Gen4 EJ25 engines which have low kilometers. 

So my question is will the current Gen3 reconditioned heads fit on the Gen4/5 short block without modification? and will i be able to perform a simple engine swap from the current Gen3 dud to a gen 4/5?

Thanks heaps in advance.