who has a 3spd manual (SAGINAW) with overdrive ?

[19673ontree]

I am in the process of trying to get hold of one , A friend of mine has a good one and was going to use it in his car but he got a muncie 4spd insted so he is probably gonna let me have the saginaw 3spd overdrive now ,
anyway who has one and how much did it help ?
problem is my 67 has either a .373 or .410 ratio rear gear and it run's it to death out on the highway , it fine for around town but when I go down to TN it's too low , thank's ,,,,,