8.75 Axle - 741 / 742 / 489

Guys,

Can someone give me some background on why there were 3 different 3rd members offered on the 8.75" axle? What are the differences between each one, and what were the determining factors that put them into different vehicles?

Long term, I will swap out my Slant 6 with a 340. I will swap my 7.25" for an 8.75". I may have found a 742 open axle. If I get this, will I need a new prop?

Long Term, I will also want to make it a sure-grip axle. I believe that all I have to do is replace the open center section with a sure-grip center section, or replace the open differential with a sure-grip differntial using the current open gear set. An I missing anything? I do not want to get in over my head any more than I have to.

Thanks,

Pete