I have swapped BBP 10" drum brake assemblies from a 7 1/4 to an 8 3/4 several times. If they fit an 8 3/4, they should fit an 8 1/4. It's been a long while since I did that swap, but I can't remember if you have to drill the 5th hole in the bottom of the backing plates or not? If what
@TrailBeast suggested above also gives you a parking brake, that would be my choice.
:thumbsup: