Rear-axle assemblies

[mikeg]

I am doing a 71 Challenger convert from a slant six to a 440 and 727 tranny. The idea is for this to be a street rod so I want some off the line punch. The current rear-axle assembly (3rd member) has the casting number 2070741. I think I want to go with a sure-grip 3:91 or 4:10. If I find a 489 or 742 will it fit into the unit or will I have to go back with a 741 unless I want to change units? Any suggestions would be greatly appreciated.

[hemi-1]

489 and 742 will fit with no other changes. Only problem you might have is a possible mismatched u-joint size between your driveshaft and the replacement chunk. But you're probably going to change driveshafts anyway. If there is a mismatch, you can use a special 7260/7290 combination u-joint available from most any parts store.