7.25 to 8.25 swap? /6 to 318 swap?

So if;
(1) I just go get the 8.25 and steal me a limited slip and disc setup, would that improve anything behind a slant?

(2) If I do the above AND put this 318 in front of the 904, what would that do for me?

(3) Would I have to mod the driveshaft for either scenario?