My 5.9 AWD Jeep Grand Cherokee only gets 12.5 - 13.5 mpg intown. It probably gain a few in an A Body so I'd say equal.
The magnum heads flows in between 1.88 and 2.02 heads with there 1.925 valves. There's like a 40 hp jump from roller LA to magnum and since the bottom end is very similar it seems to all come from the heads.
And the magnum long block responds really well to just a cam intake and headers.
It's the only heads I've seen reach 2 hp per cfm with out to much work. One of the reason the magnum supposedly responds better to cam changes is it better CR but haven't seen to many measure it's actually CR. We know LA is terribly inaccurate.
Haven't really seen a similar stock long block LA build to see the difference but stock the Magnum heads seem to have more potential but ported I think you can get more out of LA heads. Since most use aftermarket magnum heads now on a fresh build it don't matter if you start with LA or magnum unless you want factory roller then you need late 360 or magnum.
