rebuilding brakes - need a bigger hammer?

66 88 FFR - and it looks like the brake have never been touched, except by salt water. Slave cylinders rotted on their insides. ugh.

I'm trying to take things apart to degrease and wire brush, and give a coat of rustoleum for future protection.
I unboltedthe brake backing plate, and the front spindle assembly seems to be solidly attached to it.
I've soaked this baby in cleaning fluid for a few days, and it doesn't seem to want to separate from the backing plate.
Is it necessary to separate it in the first place? Or should I whale on it with a bigger mallet?

Many thanks

that backing plate really should be separated, cleaned etc. you have to make absolutely sure all the fasteners are undone. 2nd, time providing you could use a quality product like KROIL which works though it may take a day or two and 3rd. secure the spindle in something that won't move and you should be able to get a wedge between those two surfaces started, if you can see a little movement at any one spot you've got it made. You MAY find the top side easier to break first but who knows?
good luck and once you get them seperated, cleaned, painted and begin re-assembly you'll be glad you did all this rather than wonder what the metal condition is like there where the sun didn't shine.