A 3G Hemi:
-doesn't add weight. Similar to aluminum headed LA.
-does improve reliability.
-has factory serpentine belt.
-is much wider than an LA motor and is an extremely tight fit in an A body (tons of room in a B or E body).
-easier and cheaper to EFI 3G hemi vs LA.
-new fuel system required (range: $250-$2000+; $250 works fine, ~$600 gets you a new tank with everything from tanks inc).
-a built 3G short block / long block are similar in cost to a built LA motor (or cheaper, if you decide to go hydraulic roller in the LA).
-doesn't leak.
-does require new headers, engine mounts, and pan.

If starting without any parts, it's not much more than a built carbed LA motor. The real issue is the tight fit in an A body and the extra effort that goes with that. IMO, that's a sufficient reason to not swap. But you already know I swapped anyway (pulled W2 headed 408 to go 3G hemi, now on my 3rd 3G hemi in this car).