I'd need to see what it's connected to on at least the Mac side of the house to venture more than a speculative guess but my first thought is that the 7474 flip-flop IC is being used to convert the Mac's direct horizontal drive output into a standard horizontal sync signal. Buried somewhere on these forums (in more than one place, I'm sure) is a link to a page that explains how the Mac's analog board circuitry has a number of shortcuts on it compared to a "complete" stand-alone monitor; if the Lisa's monitor is more "feature complete" you'd need something that does that.
(Search for posts about DIY "Hackintoshes" in the old meaning of Hackintosh (or "HackMac") vs the current meaning of the word.)
(Search for posts about DIY "Hackintoshes" in the old meaning of Hackintosh (or "HackMac") vs the current meaning of the word.)
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