!2 bolt wlll hold any warmed over big block (and in stock form it is half again stronger than a FORD nine inch rear end). You are confusing those Strange, and Moser, or Currie rear ends for a Ford product which they are not. A stock 8.5" ten bolt is on par with a Ford nine inch as found in a salvage yard in terms of torque capacity.
The strength of the rear goes down as the gear ratios goes up since it is ultimately torque that breaks a rear end, not horsepower. So as you add torque multiplication by installing a deeper gear, the axles have to grow in spline count to keep them from breaking if you ever find traction. On the street, with street tires and gearing, you will not break a 12 bolt with even the strongest BBC that Chevy ever produced (460 horse 454 only put out 490 ft/lbs of torque).
The PowerGlide won't last behind a BBC or even a hot small block Chevy without a full rebuild and a lot of aftermarket parts thrown at it (hardened input shafts, steel drums, sprags and output shaft for starters). The factory only used a TH400 behind a big block.
Everybody loved the idea of a third gear so much GM reworked the TH400 by making a 4/5 scale model of it and called it a TH350, and then promptly stopped producing the powerslide as demand for it fell off with the new TH350 in the mix. Once again do not let those race cars running Glides influence your decision there as they don't use a 'glide at all but a B&M, or TCI or J&W or some other aftermarket hand made with all aftermarket parts tranny. It is a PowerGlide in name only.