Kelsey Hayes Disc Brake Upgrade Question

A 9" drum should work fine... I think. Just not as fine as a bigger drum;-). I bet you'll be happy, but you will not get launched through the windshield with K&H. You should also be able to aquire the correct MC for that set up. These are manual or power?

It’s my understanding that the stock 10” rear drums should at the very least have the smaller 9” drum wheel cylinders installed to reduce the sensitivity.

It will be a manual system, I have the correct master cylinder for it. I am waiting on a few more parts to finish everything up.