JAC - where does the "chocolate block" mentality come from? You saying all semi-closed Deck Block EJ257's will fail? DON'T THINK SO
There has been plenty of modded UK cars with 2.5's & 20G's put in them and got 380/380 and they are still running fine after 2 years and 35K. I know this as I built 2 such cars! This power level is not an issue on the EJ257, it's only once you get past about 1.5 Bar that you need to look into Forged Pistons, etc
Your money your choice. Listen to all the advice given, seek some more, a little more after that and then decide.
Russell