thank you for your question hope this helps.
you are removing the engine oil pan. do i have this right.
If so you will not need to remove ether the transmission or plenum.You will need to remove the transmission crossmember. to give room when you raise the fount of the engine.
here are the step by step to removal and install
Drain the cooling system.
Remove the bolts attaching the fan shroud to the radiator and position the shroud over the fan.
Remove the nuts and lockwashers attaching the engine mounts to the chassis bracket.
If equipped with an automatic transmission, disconnect the oil cooler line at the left side of the radiator.
Remove the exhaust system.
Raise the engine with a jack use wood block to disperses the load. place wood blocks under the engine supports to hold the engine up.
Drain the crankcase.
Support the transmission with a floor jack and remove the transmission crossmember.
Remove the oil pan attaching bolts and the stiffener lower the oil pan onto the crossmember.
Remove the two bolts attaching the oil pump pickup tube to the oil pump. Remove the nut attaching the oil pump pickup tube to the No. 3 main bearing cap stud. Lower the pickup tube and screen into the oil pan. Lower the pan to access the oil pump pickup tube
Remove the oil pan from the vehicle.
Clean the oil pan, inlet tube and gasket surfaces. Inspect the gasket sealing surface for damages and distortion due to overtightening of the bolts. Repair and straighten as required.
Position a new oil pan gasket and seal to the cylinder block.
Position the oil pick-up tube and screen to the oil pump and install the lower attaching bolt and gasket loosely. Install nut attaching to number 3 main bearing cap stud.
Place the oil pan on the crossmember. Install the upper pick-up tube bolt. Tighten the pick-up tube bolts.
Position the oil pan to the cylinder block and install the attaching bolts. Tighten to 10-12 ft. lbs. (13-16 Nm).
Install the transmission crossmember.
Raise the engine and remove the blocks under the engine supports. Bolt the engine to the supports.
Install the exhaust system.
If equipped with an automatic transmission, connect the oil cooler line at the left side of the radiator.
Install the nuts and lockwashers attaching the engine support insulators to the chassis bracket.
Install the fan shroud.
Fill the crankcase.
Fill and bleed the cooling system.
hope this helpsif you have any questions just ask