Thanks - I re-downloaded using a slightly different method and this time it worked fine. I must have had a corrupted or missing download.
What worked for me, using a paid Mega account for storage and transfer bandwidth: Manually copy and paste each RAR link into a browser, and manually add each part to my Mega cloud drive, which then syncs via download to my local hard drive.
What didn’t work for me: copying all links at once and pasting in via Mega “Open Links” option in their sync tool. Not sure why this didn’t work, but it didn’t.
Greatly appreciate the efforts and the replies here, thank you!