1999 Pontiac Grand Prix GT 3800 series II
I just replaced the oil pan gasket. "Wow, a really fun job...lol.
I started on this a month ago and had to stop. I put all the bolts in a tray and didn't think I could mess it up putting it back on. I didn't pay close attention when taking the bolts out; I didn't anticipate being delayed a month getting back to this project. When reinstalling the pan, it appears that I am missing 5 bolts. There are 4 bolt holes beside the transmission bell housing, and those don't seem to be the same as the others. So, am I missing 1 bolt like the others and 4 bolts of a different size, or are all 20 pan bolts the same size?
I tried to find part diagrams with a detailed part listing, but I haven't had any luck. I did find an exploded engine diagram from Danrod963, but it doesn't have a detailed parts list(with the number of bolts and their sizes).
Any help for this old "experienced & forgetful" shade tree mech would be very much appreciated.

Moved from General GM Chat to Pontiac .

On my 1997 they are all the same. Yours should be too.

Have you tried threading one of the bolts that you have into all the holes to see if they are all the same?

I have seen mentions of there being metric or SAE bolts, but they are all the same per engine in the mentions (not some Metric and some SAE on the same engine). This thread has some info on this. Of note, the OP in this thread has a 1999 SLE listed as their car. If that is accurate, it would likely have the same oil pan bolts as yours.

The two bolts on the pickup tube are a different size. If you take that off to clean it (great idea while you're in there), make sure to keep those two bolts separate.