More recently, I noticed a 16 mb SD card for a whopping $2.99, shipping included, on the always help TechBargains site. So I ordered one, and got it today.
And lo and behold, it now works. I first tried to transfer the files via Card Directories, a little Palm app to place files anywhere on MMC or SD cards. Didn't seem to work, though.
After upgrading to the newest version of Power48, I sort-of learned from the README that a) the HP roms needed to be converted -- for which one needs to employ a Windows binary, and having the work laptop home proved useful for that, and b) that these thusly generated files needed to be installed under Windows too -- pilot-xfer did indeed fail.
And lo and behold, having done that, Power48 now works and I have three new (emulated) calculators.