GEnsrud covered most of it.

• lighter rotating and reciprocating weights
• More room (width and height) under the hood (A-body especially)
• Header fit, raised port heads on low deck can fit RB headers (more headers available now-a-days)
• Low deck main webbing seems to hold up better than RB
• 400 stock bore 4.342, 440 stock bore 4.320, 383 stock bore 4.250

I love my 511 CID low deck (4.250" stroke x 4.375" bore) in my 1969 Dart.