The more I look at this, the more mysterious it is. It looks like there were at least three versions of the early balsa Astron Alpha. In April 1966 MRN, the photos clealy have the 1.29" tip, 1.6" span, and 2.8" sweep. This is very close to the SP-25 pattern. This model had the RA-2050 rings since the AR-2050 was not released. The later catalog version had a 1.44" tip, 1.49" span, and a 2.58" sweep. The later die-cut version had a 1.23" tip, 1.68" span, and a 2.78" sweep. The fins were all different on the die-cut sheet, so the averages are given.
The first published fin span of the Astron Alpha in 1966 was 4.2" which matched the 1.6" span fins (1.6" * 2 + .976"). In 1966 the published spec for the fin span was changed to 4.0" which matched the catalog version of the fins (1.49" * 2 + .976"). It is interesting that most of the photographed models in the catalogs during the early 70's used the catalog version of the fins and not the version that was in production at the time.
The later die-cut fins were the largest of the group, but the earliest fins made the Alpha 12.3" long instead of the 12.25" that was usually published.
I went with the catalog version for our FES-K25 fins because they were the best known. I should go back and release the FES-K25F to match the 1966 version and the FES-K25L to match the later version. The later version should have all three slightly different fins to match the original die-cut sheet.