Yes, the slant 6 was one of the best engines Chrysler ever produced, but would be considered an outdated design today. The motors would run forever with no major failures, but the valve guides had a tendency to wear out over time (bellmouthing), and then the car would burn oil at high mileage (maybe 170,000 +). The valve seats on the earlier heads were not hardened - which was fine when leaded gas was available (and would last forever), but later when only unleaded was available the exhaust valves would recess into the heads over time especially if the car was driven hard at highway speeds.
As for a lighter version, Chrysler produced an aluminum block version which was considered a success from an Engineeering standpoint, but I think was expensive to produce and was dropped. The Aluminum Chrysler slant 6 incorporated cast iron sleeves while the Chevy Vega had a solid Aluminum alloy block which did not last.
http://www.slantsix.org/articles/dutra- ... ck-sl6.htm
http://www.moparmusclemagazine.com/proj ... index.html