9" vs 10" drum brake spindle question

Do yourself a favor and get a kit based on production parts and the next time SSBC or (insert name here) Brake Company goes out of business you won't be SOL trying to find proprietary maintenance parts.

This kit is very popular and @DoctorDiff is a member of this forum. There are many, many satisfied customers here.
10.95" Front Disc Brake Kit (Stage 1)

The above kit will require you to use 4.5" lug pattern wheels. If you must retain the 4" wheels, find a Kelsey Hayes OEM setup and use that. They are frequently for sale on here. Or start a "Wanted" thread.