trying to see if I can get a "low mileage" JDM 2005 style EJ253 and swap the AVCS heads over to it to use in a 2008 Impreza.

Heads and all the associated gear will move over to the replacement block regardless of where it came from. 

The thing to check out is any differences in the pistons that may affect small things that may or may not become an issue. Sorry I can’t be more definitive on that front, I haven’t played much with the later model engine blocks so don’t know for sure. 

Cheers 

Bennie

yeah that was my concern reading anything I could find. The head will fit but no idea on the piston design between the two. Given they look almost identical other than the AVCS I would hope they didn't change anything else but no clue. I don't think the owner wants to take the chance so he will probably try a shortblock already done.