I ran a 3.91 equipped 741 behind a pretty stout 440 in a 71 RR and never had any issues. I've seen a couple 741's break and neither broke the pinion, both broke teeth off the ring gear.
I'm with crackedback, the myth of 741's being weaker than 742's or 489's is horse ****. The smallest part of the pinion shaft is the splines and if they have the same spline count they are the same size regardless of the carrier. I'm sure someone has broken one there, but I haven't seen it.
