easiest way to differentiate between SM420 and SM465 is the 420 only has one PTO outlet (driver side) and 465 has it on both sides.

Later versions of the SM420 had two horizontal ribs cast into the passenger side of the case so, just because it has some ribs on it, does not mean it is not an SM420.

The link Grigg posted has lots of info on these transmissions and how to identify them.


Mike
1955 Chevy 6400 ex-flatbed (no bed now!) sold September 2023
In the Stovebolt Gallery
1958 Chevy 6400 flatbed W/dump
In the Stovebolt Gallery
1959 Chevy Suburban Owned for almost 20 years, Daily Driver -- sold May 2016
In the Stovebolt Gallery

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