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Need some direction from the masters everything GTO...

I picked up a project that was in process of being converted from auto to 4 spd. Current set up is 455 w/ Muncie M-22 and 12 bolt rear.
We measured from the end of the output shaft to the center of the rear diff. That’s 57”. The driveshaft is short for this combo.
Does the automatic have a keyed output shaft? This yoke has a keyed part of the teeth in the ID. This Muncie does not have a keyed outputshaft.

So, what is the correct driveshaft and yoke?

Any input is appreciated
 

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Following are stock driveshaft lengths, all are measured center to center of the U-joints:
I
-'68-70 Muncie 4 speed : 56.00"
(small output shaft Muncie, has 5 bosses on tail shaft hsg for alum shifter mtg plate)

-'71-72 Muncie 4 speed: 55.375"
(large output Muncie, has 3 bosses on tail shaft hsg for steel shifter mtg plate, uses Turbo 400 yoke)

- '68-72 Turbo 400: 55.375"

Note, both the '71-74 Muncie 4speeds and factory Turbo 400 A-body driveshafts use the medium length '67-74 Turbo 400 yoke with 3R ujoints. GM saw fit to use many different versions of the Turbo 400 yoke, there are at least 2 versions of the long style Turbo 400 yoke, as well as a version of the late '70 's short style Turbo 400 yoke, these should not be combined with above factory length driveshafts.
 

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I know this is an old thread but it has relevant data for the swap i'm planning on.
'68 GTO-I'm swapping out the Turbo 400, installing a 200-4r, my current driveshaft is the 55.375". According to this article the 200-4r is 11/16 shorter than the Turbo 400.
Transmission Swap - Installing an CPT 200-4R In A '66 Chevelle - Car Craft Magazine - Hot Rod
From other readings the Turbo 350 driveshaft will work because its the same length as the 200-4r, which is also the same length as the Muncie small output shaft and the measurements above support this.
Putting all this together i'll need a slip yoke, 5/8" longer than my stock Turbo 400.
Any one have measurements on a stock Turbo 400 slip yoke length form center of u joint to to end of slip yoke?
 
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