An interesting situation, in many ways. If I were you, I'd just make deadlift my primary lift. I'd vary the reps and sets, and don't try to program it in a linear fashion like squats. Go to a weekly programming that has you PR every Monday and Friday on the different reps. It won't work as well as the squat, but it will be better than nothing. McCallum is probably right about your bodyweight, but that won't happen without the squats, so just do what you can on a 3 day/week DL program.