If you still have a stock driveshaft you shouldn't have an issue.
My problem was that I had already converted to a 4L60e trans, and had a driveshaft custom built, with the measurements with the stock lower control arms on it.
Just after that, I put in tubular upper and lower control arms, and the driveshaft wouldn't fit.
So my advice to everyone is... if you're going to have a driveshaft custom built, make sure you have new bushings, control arms, whatever you're going to do with the rearend, before you take the measurements for the driveshaft.
Edit: My problem wasn't caused by the control arms, it was caused by the fact that my original bushings, although they looked fine (no cracks or anything), they had actually compressed to the rear about 3/8", so my measurement for the driveshaft was about 3/8" too long.