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Things published with a typewriter but about something else should be published in !typecasts@sh.itjust.works
IBM electric was the one you'd see in a high end office. If he's got an IBM he's a serious businessman or a well paid writer.
Most companies had a variety of models, so you could just say he'd acquired a 'top of the line' model and gotten rid of the 'high school kids' ' model he'd been using.
Or you could say he'd gotten rid of the pawn shop typewriter he'd been using and picked up a fancy one at Macy's. In those days, Macy's would have been considered pretty fancy.
IBM made the Selectric, which was a pretty popular line.
Underwood was pretty much the main US maker up to the 60s. They started to hit major competition from Brother and Seiko in the mid to late 60s, but it would have been normal for most people to know that "Underwood" was synonymous with "a typewriter".
Since Underwood is one of the OG makers, you might do fine to describe an older Underwood typewriter as a boat anchor rather than just being a poor man's typewriter. It's definitely a "common man's" typewriter pre-70.