Wanting to put an overdrive into my 85

[rs74]

I am contemplating switching over to overdrive. Most of the obvious choice's would be the 700r4. I have been thinking about a 2004r trans since I hear they will bolt right in place without moving the crossmember or mount. I am also under the impression that the lockup and tv cable will hook right up without any conversion. Can someone elaborate on this a little more.

Does this sound right? My 350 is a very mild build and just wanting to get a few more mpg's out of it. I don't know much more about the 2004r other than what I have read and posted here. Is the overdrive gear its own gear or does it run off of the drive gear. What I mean is if the 2004r is installed then will I need to get an overdrive steering column so I can have a 4th gear selector position versus the Th 350 only have three forward drive positions on the column.