Roosie, I suggest you change engine builders then, as his advice is completely wrong in respect of a normal YB engine. Having an offset pin reduces piston wear due to reduced piston rock at low rpm, and hence reduces noise! It won't make the slightest bit of difference in power either! Your engine builder is a clown to suggest running centre pin pistons in a YB!

Edited to add, there are some minor benefits to centre pin pistons for engines of 10K rpm upwards, which rather rules out 99.9% of YB's!