How many 8 3/4" 3rd members do you currently have ?

Likely the reason you never broke one is because you never have drag raced. Or don't. I wouldn't see one breaking with street tires. Try this a couple dozen times: First get some big Hoosier wrinkle wall slicks, do a nice fat burn off in a wet box until there's smoke rolling up into the telephone wires. Then creep up to a surface that if you walked crossed it with your tennis shoes you would probably lose a shoe.. Then rev your dual-quad stroker up to about five grand and sidestep the clutch... (Of course I would expect you to have a 489 case spooled with all the best brand new parts set up by a professional)
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Where there's a will, there's a way...
There are a ton of 10 second cars using 8.75 rear ends that race season after season.