JIm,

The first link that I posted above is from Best Gasket for "Rear Main Seal - rubber, 56-63, Chevrolet 235"
]http://www.bestgasket.com/engine_catalog_years.asp?YearsCID=1953-62,%20235.......[543]

Many of the modern 235 and 261 high-pressure engine gasket/seal sets supply both styles of rear main seals.