Technical Question on Saginaw 4 speed Overdrive

Today I took my '63 Biscayne in to have the Saginaw (4) speed converted to add an overdrive. First time out of the garage from this rotten winter.
I have the Saginaw (3) speed overdrive unit for the conversion, and have the directions obtained from the HAMB on how to do it.
Question is:
Can I have them install the (4) speed tail shaft back on the (3) speed after the conversion, making a usable (3) speed transmission ??
Thanks for any info..
I am not going to fool around with overdrive linkage, just having them install an electrical switch to use the overdrive.
Real anxious to have this done, and will post the RMP differences/etc. when I get it back.
Right now at 60mph I am running about ~2900-3000 rpm's with a 3.73 rear end.
I am hoping to drop that down to about ~2200 rpm's for highway driving.
Currently getting 12-13 miles a gallon depending on how I drive it.

 

Although I can't answer your question regarding the extension housing "for sure", but I think it will work, there is a very detailed article on the Saginaw 4-speed with overdrive conversion in the March 2014 edition of HOT ROD DELUXE magazine. It's well documented with photos, something I've not seen much of in other articles. Butch/56sedandelivery.

 

I am pretty confident that it will work.

I hope the OD does the trick for you

 

Thanks !
Will get a copy of that .

 

be sure to let us know how it works out please!!

 

The only real linkage (besides the rods and shifter for the 4 speeds and reverse) will be the cable or a mechanical rod linkage to "lock out" the overdrive. That should be an easy task. The shift linkage will probably be the most work, as the solenoid will interfere with linkage rods and the tailhousing won't have bolt hole bosses for the shifter mount. There are bolt-on/clamp shifter mounts for the Saginaw 4 speed. Don't be afraid to consider the original wiring set-up for using the overdrive, as designed. It's fun to drive in original configuration, and there is less chance of wrecking the system. You will really only have a useful "overdrive" in 3rd and 4th gear, 4th gear probably being the most useful for a RPM drop. Repro wiring is available or can be done easily. A relay and "kick-down" switch will work from aftermarket parts or even Ford, GM and Chrysler overdrives from the 50's and 60's. All in all not an expensive or hard endeavor.

overspray

 

The output shaft from the 4 speed will need to be installed in the 3 speed tranny then the tail housing from the 4 speed.