[Dan Case]

I haven't worked on but a few of the R-3255 series but I have worked on many of the R-3259 series. (In Holley® engineering literature the R- prefix means what you see as the "LIST-" prefix stamped on air horn.)

The -1 suffix in a part number means a functional revision or revision set of some type. It could be just jets and metering blocks or they could include some other subtle design change. In the case of the R-3259 / R-3259-1 assemblies a subtle difference most won’t notice is an additional air passage to modify the vacuum secondary operation timing and rate over the original design.

To thoroughly answer the question of differences the Holley Variable Specification manual and two (unmolested preferred) carburetors for examination would be necessary. The manual is the easy part, got one in my office. Does anybody have one of each R-3255 / R-3255-1? If so check to see if the R-3255 has one vacuum pick up (small hole inside right front bore near venturi towards the back right of the bore) for the secondaries and if the R-3255-1 has two (one like above and a similar hole in the right rear bore) as that detail will not be in the manual.

My 2¢.
Dan