Rust between the wheel center and rim is quite difficult to remove short of breaking the wheel apart which is not easy at all.
Look for some better used wheels is probably best option.
Some sand blasting and something like POR15 might do a reasonable job on what you have.
I know blasting and Powdercoating won't seal the existing rust in, as I have a few wheels like you describe, thankfully not very bad yet. I am working on a replacement set though.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-