Blue Prints/Drawings forget it, think they're stored in Fort Knox at least that's what Crossroads/Keystone would lead you to believe.
As for your AC filters, they are just little black foam pieces in the four cold air returns. Pop out one and you should find it. Just wash them out, let dry and put back in.
Michelle & Ann
2018 Chevy 3500HD Crew Cab High Country DRW, D/A, 2016 RW39MB, Dual ACs, Auto Level, Auto Sat Dish, Stack W/D, King Sleep #, 17.5" Sailuns w/Disc, MORryde IS & Pin, Comfort Ride Hitch, 5.5 Onan, Res Fridge & Induction Cook Top