Do the SLDL as intended instead of conventional deadlifts, it will help your squat go up and is not as hard on your lower back and hip joints if doing it 3 times a week. Just do SLDL and squats until you moving some decent numbers well over 100kg and your regular deadlift will be strong as a result of these lifts being strong.
I throw some dips in at the end after the bar bell curls once or twice a week, its not over training as long as you are getting enough sleep and food. Maybe in your case, do BB curls Monday, chins Wednesday and dips Friday if you want to keep it at 24 sets total volume?
In all honesty the program is fine as is, dont complicate it.