Regadring this comment from GM:
"The structural oil pan is cast aluminum.... The alignment of the structural oil pan to the rear of the engine block and transmission bell housing is critical."

The oil pan has 10 short bolts and 2 long ones - how can the "alignment" of the pan be changed from wherever it wants to be? Do you put in all pan bolts loose, bolt up trans and then tighten oil pan bolts?

 

I always put the bolts n and leave em loose, then eye-ball the edges of the pan to c if it is basically straight, then torque em down in up-down kriss-cross pattern, i always double check the bolts after i get em all torgued! The only time i've ever seen a pan get busted is when someone over torqued the bolts!

 

I've had my engine apart twice both times i left the oil pan bolts loose got the timing cover on with loose bolts and rear cover on with bolts loose then with a 1/4" drive socket start to sung every thing down in their torque sequence. After that I torque them to spec's. Havent had a drop leak out ever.

 

I've not taken the timing cover or rear cover off. My concern is the relationship of the pan to the trans as mentioned in the quote from GM.

 

Its not that hard guys, use a straight edge to align the rear of the pan to the rear edge of the block, torque the bolts to spec. GM has a tool that helps align the pan but if you pay attention you can do it easily without the tool.

The "structural" part of the quote is there because the original intent was for the engine and trans to be one unit to eliminate some of the noise, vibration and harshness (NVH). Aftermarket pans are used all the time with no issues. If using the stock cast aluminum pan just get the rear aligned right and your good to go. If you slack off on the alignment part you could either break the oil pan or bellhousing while tightening the engine to trans bolt.

 

I left it loose until my trans was in place. Then snugged up the trans/oil pan bolts... And worked my way in criss cross patterns to torque.