Latest Update. I got it working!
I installed a fresh OS2.1 on an A600HD with 4 MB of PCMCIA fast memory. My last disk (Fonts) had an error, so the install script didn't finish. Fortunately, this is an Amiga, and all is well.
Had it been a Mac, the OS would not have validated and never have been allowed to work from the HD.
Next, I commented all the original OS files (in C:, Libs:, etc) as "Original OS2.1" for my own tracking purposes. In the future, any files without this comment are obviously new.
I then added empty directories to my 2.1 partition that mimic those locations on an OS3.1 install.
Classes/Datatypes/ & Gadgets/
Devs/DataTypes/
Locale/Help/
Storage/DataTypes
Next, I installed BWB 3.4 (The last version I wrote to floppies. I should have used the last release). The install script executed without a hitch.
The following BWB additions need to be removed/replaced, since they are NOT 2.1 compatible:
Finder, FullPallett, IconAppearer, and UnixDirs3. The Speak-Handler needs to be replaced with the last one Commodore included with OS1.3 or 2.05. The new Prefs/WBPattern needs to be replaced with the original from OS2.1.
Finally, I think HELP: needs an assignment in the SS since it didn't exist before.
Everything I have tested works beautifully so far. I am pleased. Thank you Gulliver!