use C20XE pistons (astra gte/gsi redtop non turbo)
they are forged psitons as std,
the block will need boring, and use new piston rings


thats the "old" way that it use to be done, but tbh im pretty sure some std rods and pistons from a focus RS could be picked up cheap enough.... and theyve been proven up to 400bhp.... (on a completly std engine with just bigger injectors and a hybrid GT25 turbo)