What I actually ended up doing was to use the Export Collection feature in FontBook on the iMac. I then had two folders on the desktop: Computer and User. I next opened FontBook on the MacBook Pro and compared what it had under User with the exported User folder on the iMac desktop. If the font was in both, I deleted it from the exported folder, eventually leaving only fonts NOT on the MBP. I then had the MBP FontBook add the fonts from the folder on the iMac desktop. It did so, and identified one major corrupted font (which wasn't added). I did the same thing with the MBP Computer collection and the exported iMac Computer collection.
So both iMac & MBP basically have the same fonts on them now. I also compared the FontCollections folder on each computer and found one entry in the iMac folder that wasn't in the MBP folder; a drag & drop fixed that.