I'm looking at the 2012 chart for the 747-8F which is quoting about 10,100ft for an MTOW (448 tonnes) take off. Flying to Los Angeles some weight will likely have to be shed for extra fuel and this will be made worse by Prestwick being a little shorter than the required runway length. It maybe that their engines have been up-rated since 2012, someone might know.
That is why I am saying that GLA will need runway work before it can match Prestwick as a heavy freight base.