A book I have on the 4.6 ltr modular said the main clearance on the aluminum block is under 0.001" when the temp is below zero. (This is based on my memory of reading the book). The author made a fairly big point that owners need to be very careful keeping the rpm down until the engine warms up.
I'm sure the bearing gap increases with temp on both the mains and the cam. No doubt in my mind that an aluminum engine would see a greater drop off in
oil pressure, when warm, than an otherwise identical iron engine.