I have a 1964 Nova sedan that i'm thinking of converting to an automatic overdrive. The car has the stock 194ci 6 cylinder engine with the manual shift 3 speed. Not sure of the rear gear ratio. A past owner moved the shifter from the column to the floor. It had a set of later model buckets from a camaro that I ditched in favor of a stock bench seat which I'd like to keep. Normally, I would just keep the stick shift because its original and I like the floor shifter conversion that clears the stock seat just fine. The problem with this transmission is that it is the older non-synchronized type when it comes to down shifting. I can foresee that double clutching would get old real quick for me. I've got a fully synchronized 3 speed located in a nearby salvage yard thats out of a column shift 1966 buick with a V8. I figure since its a GM product that it should bolt right into my nova. I'm just not sure of the gear ratios and if that would pose any problems along with any differences in case size, length, shifter mount and crossmember mounting. I've considered using a T5 from a 4.3 V6 S-10, but i've been unsucessful in locating one locally.
However,I have a 200R4 overdrive automatic in my possession that I've thought of installing. It has the converter, flexplate, TV cabel, filler tube and slip yoke with it, so I don't think I'm missing anything. I removed it from a late 80's S-10 truck with a 4.3 liter V6. I've seriously considered using it since the cost of gas has been so high lately. Will the stall speed of the stock  converter on this transmission work with an older inline 6 cyl? Or would I have to go and obtain another converter? I just don't hear much on folks bolting up a 200R4 behind a straight 6. So i'm unsure of the performance or any problems of this combination. I know i'll have to move the crossmember back, change brake pedals, hook the TV cabel up, install a trans cooler and engineer a shifter linkage. I also have a short tail TH350 automatic with no converter in my parts stash thats a possiblity. I'm just a beliver in working with what you have as much as possible.
I plan on using this Nova for my new everyday car. Really..I'm on a tight budget, so I plan on keeping the 6 cyl for now and doing an HEI conversion and possible carburation swap to a Holley/Webber 2bbl progressive. I'm pretty much going for driveablity and good gas mileage right now. I know it sounds kinda' lame compared to what most guys on this site are building, but with the cost of fuel like it is..well I'm just trying to make the most of what I have and keep the enjoyment. I'll consider installing one of my V8s when times get better.
suggestions or comments are welcome. Thanks.  

I think any overdrive trans you put in there, auto or stick, will require some trans tunnel modifications or clearancing, but I could be wrong, just those early 60's cars had pretty tight trans tunnels.  I personally would hold out for a GM 5-speed (like an F-body one).  Only other issue I see is the shifter location would probably have to move for this conversion.  The 200r4 requires all the mods you mention. You could probably keep the brake pedal and just remove or ignore the clutch pedal.  Trans cooler is definately necessary, if you don't have hook ups for it in the radiator the aftermarket external ones probably aren't sufficient alone.