TRYING TO FIND OUT WHAT 8.5 AND 12 BOLTS WILL
FIT INTO A 81 MALIBU, OR WHAT COIL CARS HAVE
THE SAME MEASUREMENTS AS THE 7.5 FACTORY
REARENDS HAVE.

This may help (http://www.chevellestuff.com/tech/rear_end_widths.htm)

There is an 8.5 rearend in the G-body cars like yours, they hard to find and cost a bit. They came in the Grand National and the Cutlass 442 int he mid 80's But I have also heard of an adaptor kit for the 60's chevelle rearends to go into your car. I have never seen the kit just heard someone say there was such a kit.