"I figure somewhere around 500Mhz should be about right. "

Wow, I never knew that I could do high-field nuclear magnetic resonance (NMR) spectroscopy without a liquid helium/liquid nitrogen-cooled superconducting magnet. Protons will resonate at ~500Mhz and carbon-13 nuclei will resonate at ~125Mhz in a 500Mhz field. I have an idea for refrigerator/freezer based spectrometer. Now if I could just figure out how to build a probe that fits between my slabs of meat and film I'll be set. And how to somehow Fourier-transform the digitized signals with some leftover turkey....