Many production cast iron and aluminum blocks suffer from a design weakness of cylinder stability by nature of poor support at the upper deck area. The manufacturing process of "cast in sleeves" provides for economy of scale in low horsepower engines, but does not accommodate high horsepower, high boost, or larger bore sizes. Darton has engineered a superior patented solution by using a unique designed cylinder sleeve which when siamesed and nested, creates a solid deck of sleeve flanges held in tension, reinforcing the upper deck area and provides for individual replacement with what they call modular integrated deck (mid).
In addition, darton designs' manage and enhance water flow from block to head ...(choose a part on the right to read more)
The passenger side is the first to go as it is nearest the exhaust manifold. if your engine vibrates at idle and smoothes out when revved this is probably the culprit. you may also check to see if the two mounting bolts are intruding into the rubber of the mount. Easily replaced just by dropping the cross member, order two and get it over with! Sold each.