8.8 vs 8.5 vs 12 bolt chevy
Ok... We have been building the custom G-body rears from 73-77 and ford LTD and 12 bolt chevelle rears for years.
The 12 bolt is strong because of the 12 BOLTS THAT HOLD THE RING GEAR STABLE ON THE CARRIER... then the pinion shaft size, 30 spline axle shafts finally the housing has a lot of support ribs that are part of the casting to keep it from stretching and over heating.
The Ford 8.8 was basically a copy of the 12 bolt chevy and the 8.5 corp rear.
The 8.8 has a big ring gear BUT it is not supported well from the carrier as it hangs off the carrier flange area by about 1" at least with no other support then the gear it self. The rear is also a 10 bolt ring gear JUST LIKE the FORD 9"
The cast housing is thinner and lighter then comparable 8.5 or 12 bolt chevy rears. It also does not have the cast support ribs giving the support that the 8.5 or the 12 bolt chevy have.
Bearing caps are wider but a bit thinner cast over the top of the carrier bearing then the 8.5 and 12 bolt rears. Cap bolts are the same size but the 8.8 ford uses a 3/4" headed bolt hex socket instead of the 5/8" socket head GM uses.
Axles- Ford cars all used the 28 spline axle shafts, Yes cobra had 31 spline BUT it was independent rear suspension so it is a moot point. IT is how ever very easy to swap in 31 spline posi and aftermarket axles to strengthen that up.
Posi units - FORD fails in this department for sure. Their clutches units need help. They go through clutch super fast so if you got one expect that to go fast. Steel clutches in the GM unit are FAR superior. Ford uses a Composite material GLUED to every other plate/ disc in the pack...Kind of like brake pad lining. It is ok for the street but if your really going to get on it at the track etc. UPGRADE this area.
So again over all what is stronger? I think for what we are all using them for... any one is of these diffs is an excellent up grade for a 7.5 10 bolt rear. I would pay more attention to the person assembling the parts...That is how your going to get your strength.
Good luck on the rear diff stuff.