Can the adapter be installed in a A3000D?, the A3640 is unmodified...
I haven't been able to find any previous experiences, seems that all the people has A4000 machines 
The adapter can be modified to remove the middle socket (but requires technical skill to do it successfully). Many people on Amibay have already done this:
http://www.amibay.com/showthread.php?65526-68040-68060-Adapter-%28for-a3640-Warpengine%29-Complete-Kit-NEW-VERSION/page15This will allow the 060 adapter to fit in an A3000D. However, there will not be any space left for a heat sink or cooling fan (unless you hack a hole in the floppy drive tray). The 060 should run cool enough at 50MHz but will need some extra cooling for overclocking.

P.S. Any modification or overclocking of the 060 Adapter is at your own risk!