Interchangability

Body parts? No.
Interior? Front bucket seats could be used. Bench? Not directly.
The rearend will be slightly wider, not a problem unless your tire /rim combination is close to hitting the wheel well lips already.
Drive train parts will bolt in, but the engine mounts and transmission mounts will have to be changed.
You could probably harvest stuff like the wiper motor, master cylinder, maybe the combination valve for the brakes.
This is for F M J body only. (Below)
On an interesting note, if somebody was modifying an F body, a B body 8.75 rearend will almost fall into one of these cars. Put one perch on the locating bolt, kick the other spring a little til the rearend falls onto the other pin, bolt it down and go. Or, spend money to move the perches over about 3/16ths of an inch...I've done this twice to the Apen and Volare I had. Used the b body shock plates and got rid of those bayonet end shocks too.
I might be wrong, but I think you could use a set of B body front super stock hangers to use a standard a body leaf spring in a Volare or Aspen too. I just never got far enough along to need to find out.If so, that would allow someone to get rid of those stock springs with the oval shaped, sloppy rubber isolated front eyes.
This was my Aspen R?T when I sold it. The biggest problem with these cars is that they are heavy. About the same physical size as a Duster, but with a full tank of gas, driver and a smallblock/727/8.75, it weighed 3920 pounds. Just like a B body.
I hope this helps,
Alan627b

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