Jerry,
The 401 used a different 3-speed with a unique bell housing (not the same as yours) with an 11” flywheel, clutch disc and pressure plate. The 400-455 also used an 11” flywheel, clutch disc and pressure plate, and the bell housing is not the same as yours either.
I reviewed my 65 Buick Service Manual and your trans was used behind the 300 V8 and the V6 in 65. The V6 and the V8 300 share the same bolt pattern for the trans, and the service manual did not denote any difference in the bell housing between those two engines. However, the service manual did list the V6 clutch disc as 9 ¼” while the clutch disc for the V8 was listed as 10 ½”. The 300, 340, and 350 all use the same trans bolt pattern, and 10 ½” flywheel/clutch disc/pressure plate combination. Any of those three engines should bolt up to your current bell housing using the 10 ½” flywheel/clutch disc/pressure plate set up.
The factory shifter was called a “mystery shifter” as it was a mystery it shifted at all. Most enthusiasts agree it should be avoided if you want your trans to last. Hurst made some of the best 4-speed floor shifters, but I have not looked into their 3-speed applications. Hurst would be a good starting point for finding a good shifter. I have seen standards of that era with bench seats. Should be fine unless you have really short legs!
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Steve B.
GSCA #2173 (1986)
67 GS 525 Stg IV
66 GS Convertible
65 GS HT
63 Riv
[This message has been edited by Dr. Frankenbuick (edited 03-24-2002).]