This is what we are trying to tell you..you need to research what minimal wall thickness is recommended for proper heat disipation..this will tell you how big an OD you can bore the block out to.
Just like doing valves in a way. You get the seating surface as close to center as you can and an optimal band of 2MM..This assures proper heat transfer so you dont burn up a valve. The same principals apply to wall thicknesses and heat drawn off by the block..its all relevant and there isnt any PAT ANSWER really.
Say someone put a sleeve in and this left 5MM between each cylinder. Yes it works..but is that engine properly transferring heat at an adequate rate? Probably not when caompared to the heat transfer that 10MM will supply. See what i mean?

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