Our 1976 Monte Carlo has a 10 bolt rear end with 30 spline axles and mathematically has a 2.66 gear ratio. I want to change the ring and pinion and the speed shop wants to know how many teeth they have. Well, I put in a dang Lockright unit that clogs up the view and if I hafta tear it apart twice, well......

I know that there isn't a designated 2.66 ratio and somebody must know something so, I'm pleading on bended knee.
How many teeth and or gear ratio for 1976 Monte with optional "Highway gears"?
PS, no tag on the back cover and coil springs with trailing arms.