Changing out my towers

[bw4sale]

My '68 was originally a 6 cylinder that someone put a 305 in. They used the 6 cylinder towers so the engine sits back too far. I know some guys like it this way and say run it like that, but it bugs me. So, I'm thinking of picking up some small block towers and doing it right. The question is will I have to change anything else? i.e. Trans crossmember or shift linkage. Will my driveshaft be too short, etc? I'm currently running a 3 speed, but would like to find a 4 or 5 speed that would fit.