8.75 741 case strength?

The 741 case is plenty strong and will survive behind any street driven 318 no problem. Here's some reading material that will put things into perspective:

http://www.moparts.org/Tech/Archive/axle/1.html

Even the Infamous GM 12-bolt has a similar size pinion and bearings! by the way, I have a 741 factory SG unit that came in buddy's 69 Cuda Formula S and it has 2.94 gears.