1978 and up chrysler 904 lock up transmission good idea for a '70 dart build?

Hi I was thinking about looking for a 1978 or newer chrysler 904 lock up transmission and converter that I would like to install in my 1970 dodge dart swinger. It will have a built-up LA 360 engine installed in it that is roughly 350 horsepower. I cruise it right now around town, and on the interstate both, with the hopped up 318 and non-lockup original 904 transmission it has in it now. It has the 2.76 gearset in it now, and at 75mph, I would like the rpms just a little lower than they are, and I figured this would do it. I also was told that the 1980 and newer 904's had a wider set of transmission gear ratios, which would also help me take off a little better too, as well as getting that little rpm drop and a drop more gas mileage from the lock-up torque converter feature...Now that i'm thinking about it, I still have a complete transgo TF-2 reprogramming kit for one of these too...Does anyone have any input on this transmission choice and on a side note, the transgo TF-2 kit?? If it is a good idea, does anyone know where or who I can get one of these transmissions from??
Thanks,
-ANTHONY