My car: 1973 Plymouth Satellite
engine: stock 318 (I upgraded to a 360)

I just screwed up my transmission getting stuck in the snow... but I'm ok with that. I'm taking the opportunity to put in a 727 trans instead of the 904. But my other problem is my rear end. My car is a "one legger" and when I go through drive thrus or stop at lights if one wheel is on ice i go no where. What upgrade should I be looking in to, can someone tell me about suregrip? What rear end was stock on my car 8 1/4 or 8 3/4? It's an every day driver, but I want to be quick so what kind of gear ratios are recommended?

You can use this to ID your rear end type:

http://www.moparts.org/Tech/Archive/axle/6.html

As for gears, go with as numerically high of a gear as you can live with on the highway, 3.73-4.10 if you can deal with it.

http://vexer.com/68rt/speed.html

Most likely an 8.25 which isn't a bad deal, should be able to get a sure grip for it. 3.55 is a good street gear for that car. Of course and 8.75 rear is a more common swap if you can get one.

If you have the console shifted auto it will take some adjustment when going from the 904 to the 727. I did this and have never been happy with the 904 linkage no matter how times I or someone else has adjusted or played with it. Someday I look into get a different set-up. You will have have to shorten your driveshaft and make sure you have the correct yoke for the 727 tailshaft.

<edit> Make sure you record the transmission number and know what it came out of. I needed a front pump for my car and sure enough, I ended up with an oddball year 727 and it took awhile to find a pump.

I turned my 8.25 (8 1/4) rear into a sure grip.
I think I used an Auburn gear. I was also able to find a 3.21:1 ring gear for a slight upgrade as I didn't want to get too radical and keep highway RPMS down.

Just find a reputable guy that does rear ends (I found a mopar guy that works at a tranny shop up here that many go to). I bought all the needed parts and gave them to him to install. The only problem you might need to contend with is the application coverage for the rearend bearings and such as I think the 8.25 rears 70-75 is one style and 75 and up is another style so make sure your 8.25 hasn't been changed if you go this route.

Unless your 360 is pushing over 350 Horse power, then stick with the 904 and beef it up a bit. Just a suggestion.

Mine is a 360 with about 300 HP and the 904 is a slightly better than stock rebuild and the 904 tranny and the 8.25 is holding up fine. I also added a tranny cooler to it for piece of mind, and it keeps it real cool in summer months.

The 727 trans upgrade is a go already. Having the driveshaft chopped and balanced as we speak. Who here has Suregrip installed, and how do you like its performance?