71 Mach 1,trans swap ,C6 to Toploader

It depends on the Toploader you bought. There's two basic verisons--- big block and small block, along with different tailshaft lengths. The big block version uses the same yoke as your C6 does----31 spline. The small block uses a 28 spline. The C-6 is tail is longer than the Mustang/Fairlane Toploaders by 3 inches.

You may need to wait and measure for the correct driveshaft length in case there are unforeseen variables. Driveshaft length will depend on what length tailhousing you are using AND what yoke is on the 9" rear. The correct Mustang toploader for a 351 uses a tailshaft that is 14" in length and a 28 spline output shaft. All cases are 10" so that is not a problem (unless you found an early 64 narrow case which is also 10" but will not bolt to the back of your 351 using a stock bell housing.)

The 28 spline output shaft use the same splined yoke as a C4 Automatic. The 31 spline output shaft uses the same splined yoke as the C6. In either case, you need to know what type of U joint you want to use (1310, 1330, or 1350) with the driveshaft. The higher the #, the stronger the joint and you should use at least a 1330 style with a toploader. You must match the joint to what the yoke and driveshaft was originally built for although it is possible to match up different combinations, such as using a 1330 yoke on a 1310 driveshaft (or vice versa) through special conversion U joints.

Here is a link to an ID chart for toploader tail shafts. Tailhousing ID Chart
IIRC the C6 driveshaft is longer than the toploader so you can always have the one you have shortened, or get one custom made for the lenght you need (I think mine cost less than $150).

pushrod power said:

IIRC the C6 driveshaft is longer than the toploader.

Click to expand...

The C6 diveshaft is shorter than a Mustang/Fairlane Toploader. A C-6 is a direct replacement for a Galaxie Toploader as far as length goes.

Yep, you're right. I had it backwards. Getting old and the memory is the first thing to go.
Driveshaft