Sears' main bike supplier was Murray, from 1938 through the '70s. But, by the early '50s, they were needing small runs of bikes to keep stores fully stocked. That's when you start to see off brand JCH's, starting with Monark, CBC/Ross, Westfield/Columbia, and Stelber. Huffy bikes begin to show up in the '60s. These bikes rarely show up in the catalogs, and were low or mid-line models. I'd bet the OP's Mainliner is one of those. I see the remnants of a V shaped decal on the head tube, likely a JCH decal. One thing I've learned over 40 years of old bike tinkering, is never say never! I've seen many bikes that 'shouldn't exist', but there they are! And the JCH name doesn't unilaterally disappear after '63. On the deluxe bikes, yes, but it took a while to use up existing parts.