The Merz is super cool and rare too, $33 is a steal. The Merz only fit rings with a 100 mm BCD, which back in the '70s was limited to only one size, 36t, until Jim made his in 32t and 31t.
In modern times, a few people (myself included) have made 100 mm rings in 30t, and I made one in 29t.

With the baby boomers aging out of racing gears, there's an increasing pressure to convert '70s full-Campy racing bikes to lower gears, and this (or the Mikkelsen) is the OG way.

Well, another time-tested way BITD was to drill the 5 spider arms at a suitable BCD for some small granny, be it 74 mm (Sugino AT), 86 mm (Stronglight 99) or 100 mm (Campy Record triple). There were even a few others like Tevano, Gipiemme and Assos that had their own wacky bolt circles — avoid those unless you have a stack of chainrings to fit.
With the drilled spider method, you don't use a triplizer middle ring, but you need some sort of stand-offs or spacers to hold the granny the right distance away from the spider.