+1 for starting both butts at the same time and taking off the slicer first.
For sliced pork I would pull at 165 to 170 Internal temp and let rest until the second one is ready.
For the pulled pork, take the butt to 195 internal and let rest for an hour. If you cook at the 275 to 300 range and foil it at an internal of 160, you should be looking at about 5 hours (ish) of cook time. Using that method with a 9.5lber took me about 5hrs and 45mins so an 8lber should be around the 5 hour mark.
Also, don't foil the slicer. Just let it ride on its own until it hits the 165-170 mark.
18.5" OTS, 22.5" OTG, CB Silver(Rip), Vintage Coleman Bullet, Pit Barrel, UDS