If you are considering switching to the muncie because it's lighter, based on that alone, the advantage would be negligible. Strength, yes, the muncie has it. For a cruiser like mine the saginaw's one advantage may be that you have more gearing options due to a wider range of gear sets.
'67 rs - ordered new by my Grandfather
327 L30, K-K, Deluxe int, tach & gauges, 12 bolt posi, 4 speed. the Melrosers - L30 327/275hp