I definately wouldnt do them on the same day. I like to go all out on the compound lifts. Squats arent a specialty of mine, and I dont even do them too often, doesnt feel right for me. So Id pick deadlifts over the 2 movements. Id hit squats on your leg day, and deadlifts on your back day. Try to hit squats within a day or two after deadlifts so that the soreness in your legs is gone by the time you deadlift again. Otherwise squats and deadlifts can interfere with eachother. Most all of my back mass was built off of heavy rows, lat pulldowns, chin-ups and upper back specific exercises, deadlifts gave me thickness in the waist, and traps mainly. Maybe some thickness in my mid back, but it didnt show up on the measuring tape. They also gave me alot of deadlift specific strength. Not a necessary movement in my opinion, but it might be good at your level to develop thickness. I was already plateaud in chest/back size when I started deadlifting consistently. Best of luck with your training