I would not pin the bores... they will still warp..

if you are going to go to the trouble of making power with a 257 which can be done. you need to strengthen the block..

1. Close decking is a must.
2. Flange top sleeves.
3. Torque plated
4. Big head studs (14mm i think i used).

the ej22t worked so well as it was a solid block (although they had water jacket galleries)..

I havent had any heating issues with my 257 that i can recall.

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