Technical Saginaw 3 speed w/ 3 groove input shaft

I’ve got a 64 C10 that I want to replace the original 318 3 speed with a Saginaw 3 speed I have found. It has the 3 grooves on the input so I think it has the 3:50 low first gear which I want. I like the idea of the lower first gear and it being synchronized in low which the 318 is not. I attached a pic of the unit. How many mods will this require to swap this “189” Saginaw for the 318? I ***ume the driveshaft will need to be shorter but will the shift linkage work? Also is it possible to put an R10 overdrive behind the Saginaw I have found?

 

Here’s the link to info above https://www.advanceadapters.com/4-saginaw-3-4-speeds

 

I've added overdrive to a full syncro Saginaw years ago. I remember that I had to replace the output shaft with an overdrive specific one (shorter).

Gary

 

No idea what power you’ve got, or what your use is. But by the time you get a user friendly rear gear in for the o/d, even something pretty high (like 3.0), you’ll be shifting into second in the Safeway parking lot. I made that mistake a few years back.

 

As above, the idea with that trans is you don't need an overdrive - depending on tire height you can get away with a 2.56 - 3.08 rear gear

 

I’ve got the 2.85 first in my Saginaw with a 3.07 rear and 29” tires. I have no problem at all leaving a stop. It will cruise through town at 30-35 in second gear easily. I’m not sure what engine you have or how heavy your truck is, but mine is a 1950 3100 with a stock 350.

 

The 318s I messed with were shorter and had a different spline for the drive shaft than the Saginaw.
To ad OD you need an od from a Saginaw. An OD output for a Saginaw and drill a hole in the case for the reverse lock out.

with the 3.50 first gear you could run a higher speed rear gear and get the same or similar affect as adding OD