When you think of it our SOHC heads flow around the same in the RPM ranges we drive in the most. And assembled SB's are getting cheaper, what you suggested has been done a member on rs25.com used a EJ257 bottom end and EJ251 heads on a turbo build. He added forged pistons and rods like you mentioned and never had any problems. Got a custom tune to handle the AVO turbo kit (the RS25 version with the TMIC and Borla Rep UEL style Up Pipe) runs error free.
Also the OP should read your WHOLE thread its been several thousands of miles and your stock 253 is still running fine!