The supplied LispWorks for Macintosh images are universal binaries, which run the correct native architecture on PowerPC and Intel-based Macintosh computers by default.
A running Lisp image only supports one architecture, chosen when the image was started. On a PowerPC based Macintosh, this is always the PowerPC architecture. On an Intel-based Macintosh, a 32-bit LispWorks image can be either the native Intel architecture or the PowerPC architecture (using Rosetta), but a 64-bit LispWorks image can only be the Intel architecture (because there is no 64-bit Rosetta.)
Functions such as save-image and deliver mentioned in Creating a new executable with code preloaded create an image containing only the running architecture and functions that operate on fasl files such as compile-file and
only support the running architecture.
LispWorks User Guide and Reference Manual - 21 Dec 2011