The disclosed multi-cylinder, poppet-valved engine, has replacement cylinder sleeves larger than the original sleeves, and laterally supported near their upper ends by an aluminum alloy plate having a continuous flange or boss projecting into the cylinder block. The flange has an inner perimeter surface having a profile fittingly engaging upper exterior cylindrical surfaces of the sleeves providing lateral support to the sleeves and heat transfer from the sleeves to coolant and to the block.