i dont know how much higher in the rpm the mustang makes its power, but the cam are only half of that, the trucks intake manifold with its long runners is responsible for some of the low end, so changing the heads and cams while retaining the stock intake is probably going to split the differance.
i think mustang cams because they would be a lot more affordable than aftermarket cams and the cam gears that can be from $550 to $750 (gears and cams). they might make them but i have not seen anyone develop cams for improved lowend (truck) application. a custom grind would be at least another $100 with no guarantee of a cam that peforms like you want.
if you did the heads with the mustang cams and the low end sufffered, there is alway the option of 4.10's. it is just my opion but the stock intake manifold is never going to allow you to make big numbers high in the rpm without a power adder. it is difficult to make big changes in power out put with out moving the rpm levels (the new 3v 5.4 makes more hp and tq but the peak output is higher in the rpms).
most aftermarket parts make the "10 hp gain" in the 4000 to 5000 range.
the big problem with all this is that we just wont know until someone does it. i havent seen any build ups involving the changes we are taling about on a truck. cosidering the cost of cams, heads, custom tune, and everything else that goes with it, it is not an attractive option to most. until you see dyno runs showing before and after, its all bench racing, which is about all the racing most of us have time and money for.