They were supposed to build a 130 to LEO rocket that should launch the first time in 2016 (min 70t) and use existing contractors. That is kind of insane.
So NASA basically allow their internal teams to come up with Block upgrades based systems and that's where the whole SLS Block 1a, 1b, 1c comes from.
The problem with this was (and is) that they had no reason to rush to a quick block 1 as there were really no missions for it.
Had they been given until 2020 developing a single core modern Saturn V would have been a much better design (this is clearly evident in their internal design evaluation documents). The had already put a lot of work into J-2x and modern F-1 version was attainable. My alternative would have been to use a whole bunch of SpaceX Merlin 1D instead but they never considered that. This version would also have been much closer to the 130 tons in the first version.
And it could have been evolved to be reusable unlike the current SLS.
What people from the outside don't really see is the NASA internal competition. Johnson Space Center clearly wanted the Shuttle derived version, Kennedy Space Center really wanted to Saturn V style rocket. Some at NASA HQ wanted to give it as a contract to SpaceX/ULA.