5-1/2 BS is what you need.
Agree but the Crager catalog only shows 3 3/4 and 4 1/4 BS in 10".
Crager used to have a custom shop but it closed.
What I used to do many years ago is buy the 15x7 reversed which.comes with 2 1/4 BS.
I would take them to a local circle track shop and have 3" added to the back side
resulting in 15x10 with 5 1/4 BS. Close enough.