Actually, I've just been able to successfully create the thunk file needed for 64-bit loadlibrary() operation.
The issue is with the OA_xxx functions in the amcd32d.h file. They use function signatures like: OA_Initialize(const char * const pcFilename,...)
The doubled-up use of const makes the compiler unhappy.
In general, the thunk-file generator for 64-bit loadlibrary is quite sensitive to syntax in header files that often worked under 32-bit loadlibrary(). In part it's because it requires strict C syntax. So generally, the header files have to be massaged to allow the thunk file generation to proceed. This was a new one for me.
In this case, those OA_xx functions are somewhat ancillary, so I just commented them out. If you need those functions, some signature change would be needed in the header to allow the loadlibrary() thunk file gen to work.