904 dilemma, please help!!!

So I'm currently in the home stretch of finishing the 360 that I've been building for the duster. And since I'm plannin on making a pretty significant amount of horsepower(400ish plus 100shot of NOS), I know I'm gonna have to rebuild/ beef up the tranny to be able to handle it. But my dilemma is that I was plannin on just pulling out the 318/904 combo thats in it and dropping the new 360/904 combo right in. But I started rebuilding the spare 904 I was gonna use and realized that its an 82' lock-up model:banghead:. So now I figure I have 2 choices which is where I need y'alls opinion.
A.) Just pull out the tranny thats in the car and rebuild it and sell the other 904
B.) Or Pull the tranny out and rebuild and swap out the lower first gear ratio from the lock up 904, also maybe use the front clutch unit since it has the 5 clutches in it, but im not sure what else i need to change to use it.
I'm getting anxious to get the motor in the car so I'm kinda leaning towards just rebuilding the current 904 and throwing it back in since that would be the quickest and easiest choice, but wanted to hear some other (more experienced) opinions. Sorry for the long post, I appreciate any input.
Thanks, Tom