Unfortunately sometimes you get burned when you try to save a buck.
The first thing I would do is pull the pan and see what the screen looks like on the pick up tube. The guy you had do the previous work would not be my first choice to have this done. Using used oil to save a couple bucks, well.... probably didn't save you any. If the oil was changed before the engine was started after replacing the lower intake there shouldn't be any issues with "cloudy" oil (another red flag) since the coolant would be the first thing to drain out when you pulled the plug!
It doesn't seem possible but there is a chance that the main bearings where trashed running the car with coolant in the oil. GM's do not like coolant in the oil!