Please Help, Removing oil pan
 

I'm new to these monsters and recently (as in yesterday) purchased a 2002 Express 1500 V6 with a spun bearing. I bought it rather cheap, with the intention of changing the bearing, and possibly replacing the engine if it damaged the bearing again. But I am stuck, I am trying to get the oil pan off, and have removed every bolt I see, except the 2 under the plugs by the transmission.

I am working based on Pdraton's thread here:
https://chevroletforum.com/forum/exp...-engine-47726/

But when I remove the rear plugs, instread of bolts (or nuts as the Astro guy describe) I found what appear to be hex, button head, screws.

Does anyone know what size they are? I have cleaned them with brake cleaner but with the mix of SAE and Metric I have seen, plus oil, I am terrified I will use the wrong size and round them off.

Thanks for anything you can offer.

Correction, its a 2001.

Please forgive a chevy newbie, it was 2 1/2 inch nuts, the allen heads I saw were for the studs going into the Rear main seal, if your are doing this job, DO NOT REMOVE THEM.