If the 4.8 is put together the same way as the 4.4, the timing cover gaskets are a 14 hour flat rate IIRC. I did this on my 2000 4.4- I damaged it when replacing the valve cover gaskets. There was a service tool required for the job- the bottom of the timing cover seals part of the oil pan. The bolt holes in the timing cover are slightly over-sized to allow pressure to be applied to the oil pan gasket. The tool bolts in place with the valve cover removed and puts the required pressure on the timing cover- you then tighten the cover bolts to maintain the tension. Clever design, but a RPIA.

Good luck with the DIY.

__________________
Dave

'05 325xi
'10 E70 35d
'85 911 Carrera
'66 911 Work in progress
'91 Chevy C1500
'95 Jeep Cherokee
‘18 Jeep JLU