See hot rod engine annual , article on free standing sleeves in 6.1 new style hemi block. Interesting and worth a look as it is exactly on the subject you are talking about for the same reason but just a different engine.
We run half bored blocks to strengthen them when we push the limits. The shorter a cylinder is the stronger it is so by supporting the lower half we can make a huge improvement in strength. Interestingly enough the engine we have been working on does not run hotter, in fact this weekend racing it never even got to 185F.
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