The google books on the Sony site are all in EPub. They don't have DRM.
To me, they look as though someone generated an automatic text file from the original PDFs at the Google site, then sent the result to an EPub converter.
As your 500 won't read EPub, you may well be better going directly to Google Books and running a conversion yourself, AprilHare. Or just see whether the PDF is readable on your 500.
PDFRead just might work here:
https://www.mobileread.com/forums/showthread.php?t=21906
According to the write-up in our wiki, it is a tool for converting primarily PDF and DJVU documents for reading on eBook devices. It does this by creating an image out of each page, enhancing the image and then collating the images in a device-specific format (supports .IMP/.RB/.OEB/.LRF/.PRC/.HTML)