This sounds like a wack idea,but I have seen A-Body cars with G-Body rear,which give the same result. The G-Body rear is narrower. Either way,you have some work to do.
If you get a grand national or 442/HO rear,they are an 8.5” 10-bolt. Same guts as what you have now. Different housing.
Gbody rear in Abody and vice versa requires either offset custom control arms from baseline suspension or the like or spherical bushings in the upper ears and the arms Gbody 8.5 rears have much smaller axle tubes and c clips,= Not good Just need to narrow the 8.5 you have , I can do one and blast and paint if you want $350 plus ship
Hey thanks fort the heads up. I might just take you up on that offer when time comes. I still need to figure wheels and tires. I will likely start a build thread seeing as I will be restoring the lark.