The skulls weren’t used in the taxidermy, they are actually part of the museum display.
The one photo of Patterson with one of them shows a pretty standard looking lion head shape.
The skins were used as rugs by Patterson so when they were sold to the Chicago Field Museum, they were really too small to be used as a full mount - that is why the legs look unusually thin and really, the lions look thin overall.
I put the long faces down to the taxidermist.