T56 has two OD's I have been thinking about putting one in my 67.

BTW which Muncie do you have?

 

Sure, then you can put 5.13's in the rear so that 6th gear would get used.

 

Its a 1968 Muncie M21

 

So finaly tonite I finished the 4 speed to automatic conversion. For those interested in doing this this is what I ran into. The things I expected was cutting the drive shaft 2 3/4 inches. Replacing or moving the crossmember and drilling new holes. I moved it. Rewiring the lockout, you can have a trans mechanic do it or buy a kit. I had a mechanic do it. What I didnt expect was the kickdown cable bracket. I bought a universal one and it needed modifying, Cut and weld. I also had to modify the throttle linkage. Bought a B&M Mega shifter. The bracket that mounts on the bottom of the trans is way off so the cable binds. Tech support for B&M told me to modify the bracket. You would think you pay $250 for a shifter you would get the right parts. Had to drill holes thru the crossmember for the shifter cable. Going over or under the crossmember binds the cable. All thats left is to fill it with trans fluid and test drive. However leaving in the morning on a hunting trip so its going have to wait till I get back. I will report back then.

 

Finally did the test drive and I couldnt be any happier with the results. With the 4 speed 65 MPH the RPM was 3000. Now 65 MPH the RPM is 2200. Cruising down the interstate now is a real pleasure and I still have the 410 rearend for those occasional burnouts. I would highly recommend this to anybody that wants the low gears and still be able to cruise at 75MPH.

 

I would change the rear gears for the 308's and keep the stick shift. It would by far be the least expensive way to go.

 

It would be cheaper, but definitily not better. By the way at 70 MPH its turning at 2500 RPM

 

What you have now is the perfect performance/highway combination.
With also having 4.10's, an overdrive is in my future as well.
I wouldn't give up the low end performance of the 4.10's for the world.