Yes. These old stereoscopic cards are already in the basic format needed: one image for each eye side by side. In most cases, you can scan the card as a single JPEG, keeping both left and right images together, and use it in a stereo photo viewer app for Google Cardboard.

A common format for this is JPS, which is essentially a JPEG stereo image. In practice, that often just means saving or renaming the scanned side-by-side JPG as a .jps file so compatible viewer apps recognize it as a stereoscopic image.

The main thing is to scan the card clearly and preserve the left/right order. Some apps may also let you adjust alignment or crop if the scan needs centering for comfortable viewing.

So no complex conversion is usually required—just digitize the stereo pair and open it in a Cardboard-compatible stereo viewer.