LOL, naturally I find the threads about covers
after I post my first comment and covers on HarryT's Tom Swift thread.
https://www.mobileread.com/forums/showthread.php?t=13638
Since HarryT's Young Adult books are among the first books I ever read I think they should have the original covers (or extrapolations) where ever possible. I can still feel the raised embossing and smell the old book smell they had and seeing the old covers in my MobiPocketReader app fills me with pleasure.
I used mobi2mobi.exe (win32)
https://www.mobileread.com/forums/showthread.php?t=17718 and Mobi2Mobi_GUI.exe
https://www.mobileread.com/forums/showthread.php?t=21763 to attempt to add a cover to HarryT's prc file for the Air Service Boys Omnibus
https://www.mobileread.com/forums/showthread.php?t=21201 with limited success. While the my cover (first below) is displayed in the MobiPocketReader's right side bar HarryT's blue cover still shows up as the icon (?) in the main display. Selecting "Cover" from MobiPocketReader/Contents also displays my cover. All rather odd.