Need help to ID my Zenith TV

[dano]

This may seem like a strange request. I have a Zenith color roundie set that is currently in storage such that I can't easily access the back of the cabinet. I believe it to be early 60s vintage, it's a basic cabinet with a flat top and sides, and legs. I have the chance to get some TV tubes for next to nothing, and I would like to identify what chassis is in the Zenith (or just narrow it down to a few possibilities) so I can save just the tubes I would likely use. I did my best to read the model number, and all I can make out is "S72". Mine it the type that uses a rotary VHF and UHF controls that are staggered, if that helps. Any ideas on what chassis I have would be greatly appreciated!