You can get a stock short block from heuberger or other online parts places like flat irons tuning. 1600-2100 bucks if recall. That motor you posted might or should work too but that’s a long block. You could save money by using all your parts on your current motor except the short block. Maybe send your heads to a Subaru specialist like ASF machine in grand junction CO to get reworked and put all the parts on the new short block.
https://www.flatironstuning.com/subaru-oem-shortblock-04-08-sti-ej257
https://www.flatironstuning.com/subaru-oem-shortblock-04-08-sti-ej257