9" vs 10" rear drums

Since it seems impossible for me to be able to find a set of new 10 x 1.75" sbp rear drums, I'm thinking it would be easier to just swap to 9" drum assemblies on the rear, since I have to completely rebuild the brakes anyway. It looks like all of the 9" parts are readily available from the auto parts store at a decent price.

Would there be a huge difference in braking power between the 9 x 2 and the 10 x 1.75 rear brakes? Am I an idiot for thinking about taking a step in the wrong direction?

BTW- This is for a 66 barracuda with discs up front. It just frustrates me not being able to find parts.

Thanks.