I probably bought wrong 8 3/4

If the perches are 43" and it has the SBP axles then it is definitely an A-Body rearend and it should fit right under your car. All A-Body 8.75 rears had the SBP axles. I apparently was wrong about the width. As for the driveshaft goes, it will be easier to get a driveshaft from a 67-72 A-Body with a 904. Shorten the driveshaft to the length you need, add the correct slip yoke for your trans. and the 8.75 u-joint and you are set.

Joe