Make sure you run a Drive Shaft Saftey Loop. If you have never been in a car when the u-joints fail as I have, let me tell you it is a scary thing.
I would definatly get rid of the 1310's, especially if they are the hollow greasable kind. If running the 1330's are get the solid ones, yea it might be a pain to drop and grease but if you race on slicks its better to have the added insurance. However since you will most likely replace the whole driveshaft by all means get the 1350's. If you have an overdrive tranny, make sure you get the driveshaft ballanced. You will have to change the yoke on your rear end since your stock rear end probably has the 1310 yoke.
david pozzi - my 3.5 inch aluminum driveshaft clears my lowered 68 just fine.