I've got a EJ253 longblock from an '07 Forester with some apparent main bearing issues. The heads have been rebuilt, so I kinda don't want to look for a new longblock (would prefer to reuse). However, I have a couple of EJ251s hanging around. Can I use the shortblock from an EJ251 and put the EJ253 heads on it to put back in my '07 Forester? Any issues or suggestions with that?

The heads will bolt on. You’ll have to investigate the differences in the piston if any. 

Other than the piston question, it’ll bolt together etc. 

Cheers 

Bennie

Awesome, thank you! Pistons I can do, just don't want to deal with main/rod bearings if I can help it.