I am familiar with 3 types of 3rd members listed in order of durability: 741 < 742 < 489. Granted, pre 1970 units had the clutch-style (easily rebuildable) carrier, but all carriers will interchange between any and all cases. Gears are specific to each case. Shape of pinion is where you will find the difference in durability due to tapering and lack thereof. If you are doing a moderate 440 auto build, any case will be fine.
new yukon 8 3/4 clutch carrier at:
http://www.yukongear.com/Positractions.aspxRear housing selection will depend on how much tire you want to fit under there. Perches can be moved and offset sheackles can be used for clearance.
You are looking at about 63" drum to drum on your car, which is one of the widest. perch to perch, you are 47.3", which is the widest of all. The path of least resistance would be to find the original stock 8 3/4 to match your car. The fender wells are quite large to fit some meathooks under there. But, e body 8 3/4 rears are likely less difficult to find and easier on the wallet? You can move the purchases a bit, but you must watch tire/spring clearance. that is where you might consider the the reloc kit or backspace manipulation with wheels.
I wouldn't get to carried away with new axles...use stock with any 5 x 4.5 bolt pattern. your wheels will fit fine. I don't think there would be a need for an a body rear...again, the rear fender flare is huge.
brakes sizes big and small with stock drums. either will be fine for your application. I believe that the 7 1/4 backing plates should just slide right off and right onto the 8 3/4...viola.
most importantly, don't forget to add oil...and a little sure grip additive.
mike
