this means that the timing will be 180 degrees off, so now it isn't okay. It will not bend valves but the car will run badly. There is an incredibly detailed timing procedure for this vehicle so taking it off and putting it back on in the same place isn't enough. I will try and copy and paste the procedure for you if the GMM server will allow it:

Rotate the crankshaft in the engine rotational direction (clockwise) using the J 42098 until #1 cylinder is at TDC and tighten the lever arm to the water pump pulley flange.

Important: Ensure that the alignment of the crankshaft is not 180 degrees off. The alignment marks must align with the corresponding notches on the rear timing belt cover.

Install 1-2 and 3-4 camshaft locks, J 42069 and J42069-2.

Inspection

Important: Failure to follow the described timing belt inspection and maintenance may result in a broken timing belt and cause severe engine damage.

1. When checking the condition of the timing belt, inspect for the following conditions and possible causes:

   •	Tooth is broken and/or tooth root is cracked -- Camshaft jamming, damaged camshaft/crankshaft oil seal and/or coolant leak, old age, tensioner not functioning properly.

   •	Back surface of the belt is cracked/worn/scratched/scored -- Excessive cold starts, tensioner jamming, overheated engine, interference with the belt cover.

   •	Side of belt surface is worn -- Improper installation of belt, overload or misalignment of cam drive components, tensioner jamming, heavy thrust loading against idler guide flanges, damaged idler guide.

   •	Teeth are worn -- Poor belt cover sealing, excessive belt tension, tension jamming, rough and/or scored cam sprockets.

   •	Clean break across fibers -- Kinked belt before or during assembly, foreign material under the belt.

   •	Oil/coolant impregnated and/or swollen belt -- Poor oil sealing, coolant leak at pump, poor belt cover seal.

   
   
   
   
2. Check that the tensioner turns smoothly and that no binding occurs in the bearing.

Installation Procedure

1. Remove the crankshaft locking tool. This will ease installation of the timing belt.
   
   
   

   Important: With the camshaft locks installed, verify the distance between camshaft sprockets with the green test belt located in the J 42069 .

2. Start at #1 and #2 camshaft sprockets, route belt around #1 and #2 sprockets while aligning belt marks to the marks on the sprockets and the rear cover.
3. Install the belt around the timing belt tensioner.
4. Route the belt around the upper idler pulley.
5. Route the belt around #3 and #4 camshaft sprockets while aligning the belt marks to the marks on the sprockets and the rear cover.
6. Route the belt around the crankshaft hub sprockets while aligning the marks on the belt to the marks on the sprockets and the rear cover.
   
   
   
7. Install the J42069-30 to lock the timing belt onto the crankshaft hub sprocket.
   
   
   
8. With the belt firmly engaged on the crankshaft hub, carefully rotate the crankshaft counterclockwise to get the belt slack on the lower idler pulley side.
9. Route the belt around the lower idler pulley.
   
   
   
10. Remove the J42069-30.
    
    
    
11. Install the J42069-2 and tighten the lever arm to the water pump pulley flange.
    
    
    
12. Perform the following in sequence:

    12.1.

    Install the camshaft checking gauge to cams 3 and 4 and verify alignment marks are within 2 mm (0.08 in) of each other.

    12.2.

    Install 3 and 4 camshaft lock, if properly aligned.

    12.3.

    Install the camshaft checking gauge to cams 1 and 2.

    
    
    
    

    12.4.

    Rotate the #1 camshaft sprocket counterclockwise to remove the slack between 1 and 2, and 3 and 4 cams.

    Important: Ensure that the camshaft timing marks are to the left (retard) side of the checking gauge.

     

    12.5.

    Rotate the upper idler pulley counterclockwise until the marks are properly aligned within 2 mm (0.08 in) of each other.

    12.6.

    Install 1 and 2 camshaft lock, when properly aligned.

    Tighten
    Tighten the upper pulley bolt to 40 N·m (30 lb ft).

    
    
    
    
13. Adjust the timing belt tensioner so that the center alignment mark is about 3 mm (1/8 in) above the alignment mark on the spring loaded idler.
    
    
    
14. Remove 1-2 and 3-4 camshaft locks, J 42069 and J42069-2.
15. Remove the J42069-10.

    Important: If TDC is passed, do not rotate crankshaft counterclockwise. This will not allow proper slack to be taken up between the timing belt tensioner and the crankshaft sprocket. To correct, rotate the crankshaft an additional two turns.

16. Rotate the crankshaft 1 3/4 turns clockwise, install J42069-10, and then stop at TDC.
    
    
    

    Important: Timing marks on the timing belt are used for initial installation only.

    Important: If the timing marks are off, repeat the procedures to readjust. Removal of the timing belt is not necessary.

17. Tighten the lever arm to the water pump pulley flange.
18. Recheck both pairs of the camshaft timing marks using the J42069-20 .
    
    
    
19. Adjust the timing belt tensioner to that the center alignment mark is about 3 mm (1/8 in) above the alignment mark on the spring loaded idler.
20. Tighten the timing belt tensioner.

    Tighten
    Tighten the timing belt tensioner fastening nut to 20 N·m (15 lb ft).

21. Verify the timing marks are still aligned.
22. Remove the J42069-10 and J42069-20.
23. Install the timing belt front cover. Refer to Timing Belt Cover Replacement-Front.
24. Connect the negative battery cable.

    Tighten
    Tighten the battery terminal bolts to 17 N·m (13 lb ft).

yes, the #1 piston does need to be at TDC