is there coating in the cylinders like the V8s? IE: alusil/Nikasil.
I dont think anyone on here has ventured into max bore concepts, I think the best you can do is get it sonic tested to see how thick the cylinder walls are and go from there. Fill it with cement and go thinner or maybe even sleeve it might be options for strength. Might be able to get some sort of stock pistons from a large bore engine with the valve pockets in the general area and custom cut them to be exact. Watch for valve shrouding with them small combustion chambers if you go to big valves but you could grind some clearance there too. You could do a lot if the sky is the limit.
95 E34 530I V2.37
===========
Those who make peaceful revolution impossible will make violent revolution inevitable.
John F. Kennedy