So, my after action report.
The proof is in the eating and we won't eat it until Wednesday at my daughter's joint graduation party. It sure looked good tho, and most of them felt right. Some shoulders were more fatty than others, and I couldn't predict by looking at the bark on them.
My plan had been to start them all at the same time, with 4 on the top rack, and 6 on the main grate. They all fit (barely) and were each in the 9-11 lb range. I put three drip pans until the main grate. It took a long while for the outside edges to come to temperature (I put an air probe between the right most pieces). But it ran smoothly.
I didn't have to stir pellets much. I started with a pretty comfortably full (not maxed) hopper at 8:00 am. Around 6:15 pm I got an alert about low pellets, and refilled. That was the last time.
I started wrapping the shoulders at some point (I forget what time) as they reached 160+. I shuffled them around to try to even out exposure to hot spots whenever I pulled one off. I wrapped by putting them in a foil drip pan and then covering with foil.
My overall plan was relatively solid. I would do a few things differently.
The first two to be wrapped, I'd go ahead and put them in the oven to finish. There's not room for 10 of these in foil pans on the grill. There would be no airflow possible. Then as those finished, I would keep pulling off and putting in the oven.
I would never carry the meat and juices in the foil pan without support under them. They just aren't strong enough. I had two spills, and one was because the pan folded. The other might have sloshed, it happened after midnight, so I was a little fuzzy, and unfortunately barefooted, so I have some red splotches on my foot (it was hot, but not too hot).
This led to another issue: immediately after this, I took a pan inside, and was checking my foot. The temp checker beeped at me while I was inside, so I checked it and went out side. Only to see that I had left the lid open and the whole right interior was flaming with a grease fire. It was really windy, and there was lots of greasy debris on the racks and foil. So I think the grill tried to heat up with the lid open and put out lots of heat, which set off the grease, and the windy blowing straight into the grill fanned the flames even more. There were a lot of flames, but not big ones. I closed the lid, and determined I should shut down the grill to make sure the grease fire would go out. After about 10 minutes I opened the grill and while there was some greasy bits burning on the bottom, it was rather contained and no risk of backdraft/blowback/whatever. (I always stand to the side and open carefully in those situations).
I checked the meat, and all but two were done (or done enough - the probe went in easily and they were over 190). So the two that were well below 190 I put in the oven to finish. Only one of the pieces was significantly affected by the overheat/grease fire, I think. The bark was charcoal flavored (or smell), so I just removed that and the inside was fine. I didn't keep the drippings for that one. When I brought that one in, the drippings were sizzling and spitting for a few minutes - the temp was well over 210 in those areas.
So, don't walk off and leave the lid open for 5-10 minutes. It's a bad idea.
Between the excitement and the late hour, I forgot to take any pictures of the grill full of foil packages. Sorry. I wish I had a picture of the flames, but I would never stop to take a picture with that much meat at risk.
I think the last two pieces were done around 2 am, so an 18 hour cook for 10 shoulders. Plus a couple hours of prep, and an hour of clean up (and I've not done the grill yet). I'm tired now.