Sum,
I am not familiar with the GM 7.5 inch rear end. What is the smallest diameter of the pinion shaft that could twist in two. That is an area where you might find the weak link.
Years ago when Flatfire was running, Speedway Engineering found a 3.5 or 3.6 ratio that would fit into the Q-change in the car. When the car started to approach the 300mph range they were starting to twist the pinion shaft. To my knowledge non ever broke, but I know they did replace one or two gear sets for those reasons.
Below is a Q-change pinion shaft from the Modified Roadster that I own. The previous owner had a blown fuel motor in the car that made 3000 Hp and 3000 Ft lbs Torque. The ring and pinion were 1-1 with Q-change gears making the final drive as I recall 1.67-1 or there about. This part of the pinion would twist when the the tires would spin then bite at El Mirage. The torque spike at that instant was too great for the minor diameter of the Quick change pinion shaft.
This car was only run at El Mirage, except for going to Bonneville once, where it ran the fastest 2 1/4 mile speed ever run at the time, but a transmission bearing keep it from possibly setting a record. The only reason I am mentioning this is that depending on conditions the traction at El Mirage can be much better than Bonneville, so if you are building a high HP car with lots of torque to run both venues, you might want to take that into consideration.
Tom G.