Last year there was a 43t chainring in 151mm bolt circle diameter on Ebay, brand was Zeus and it was from the era when they used an outer ring with the tiny 50.4mm bcd circle like TA Cyclotourist and Stronglight 49, then the inner chainring was bolted to the big ring on a 151mm circle using standard Campy-style chainring bolts/nuts....but instead of a spider arm between the rings there was a tubular spacer around the chainring nut, like you'd see on TA and Stronglight and also many cheap old road double cranks where the big ring was also the spider....this allowed the smaller 43t size since the spacer could be quite thin, similar to 41t rings in 144bcd, and 38t rings in 130bcd....on all these you usually have to file/grind the spider tabs on a regular crank, to clear the chain (if the spider bolt-tabs are standard length, the chain will sit on them and be caused to skip since it's not fully down in the ring's tooth valleys)....some crankarms already have the ends of the spider bolt-tabs cut down, a few Shimano and Sugino and some others have been seen this way from the factory...but it's easy to do yourself, you simply file or grind the end of the tabs at an angle, just enough to barely clear the chain....you use the actual ring and chain to do it by trial and error, not difficult at home.
Last year there was a 43t chainring in 151mm bolt circle diameter on Ebay, brand was Zeus and it was from the era when they used an outer ring with the tiny 50.4mm bcd circle like TA Cyclotourist and Stronglight 49, then the inner chainring was bolted to the big ring on a 151mm circle using standard Campy-style chainring bolts/nuts....but instead of a spider arm between the rings there was a tubular spacer around the chainring nut, like you'd see on TA and Stronglight and also many cheap old road double cranks where the big ring was also the spider....this allowed the smaller 43t size since the spacer could be quite thin, similar to 41t rings in 144bcd, and 38t rings in 130bcd....on all these you usually have to file/grind the spider tabs on a regular crank, to clear the chain (if the spider bolt-tabs are standard length, the chain will sit on them and be caused to skip since it's not fully down in the ring's tooth valleys)....some crankarms already have the ends of the spider bolt-tabs cut down, a few Shimano and Sugino and some others have been seen this way from the factory...but it's easy to do yourself, you simply file or grind the end of the tabs at an angle, just enough to barely clear the chain....you use the actual ring and chain to do it by trial and error, not difficult at home.