One of the auxiliary utilities included with Golden Gate is opus-extractor.

opus-extractor is a simple utility to extract the ORCA compilers, utilities, libraries, headers, et cetera from an Opus ][ disk image to your computer for use with Golden Gate. It also works with other disk images; the original idea was you might have ORCA installed on one of your disk images and could extract components from there.

One unanticipated use is installing ORCA/C updates, since they also follow the standard ORCA layout.

opus-extractor --verbose --source=/ ORCAC.220B3.2mg 

You may need to elevate your privileges with sudo or runas.

(since there are no Shell or Utilities directories on the update disk image, there is a harmless warning that those files were not found).