Strength Gains In 12 Weeks

Interested in opinions. How much 1 rep strength can a 55 year old, who has been doing more GPP style workouts, can expect to gain in 12 weeks? Starting- 5’9" 155lbs max lifts( Don’t laugh!) bench 185 press 120 chins 50 lbs. all 1 rep strict form I don’t do deads or squats due to history of low back injuries.