When Ford brought out the 4.6L back in 1993 for the new Lincoln MARK VIII luxury coupe. It was the opening of Fords new strategy of having as many engines to share as many components as possable. I'll start from the bottom and work my way up.

Oilpans 4.6 and 5.4 are interchangable the 6.8 being a V10 is to long

Crankshaft 4.6 and 5.4 are inter and the 6.8 is not

End caps and bearings can be used for all three

Connecting rods the 5.4 and 6.8 are inter the 4.6 can not because they measure 3.55 inches long and the 5.4 and 6.8 is 4.15 inches long

Pistons can be used in all three.

Heads and valvetrains and covers 4.6 and 5.4 can be interchangable as long as it's for a SOHC to SOHC swap or a DOHC to DOHC swap the 6.8 being a V10 can not use any heads or valvetrain from the V8 twins

Intakes the 4.6 and 5.4 can use each others including if the airbox is on opposite sides case in point the 03/04Marauder and the 03/04 MachI stangs use the same intakes they just flipped them so the Stangs is off the passanger side and the Marauders is off the drivers side the 6.8 being V10 can not use

Note these are just the engine parts and not any accessories