What's the difference between early and late cat delete pipes?

[deathsled986]

Are they different lengths because of different mounting locations on the two different style exhaust manifolds?

Or is it just that they have extra bungs for o2 sensors?

I have an 01 with some cheap ebay headers on it and the fitment of the flanges going to the secondary cats is less than desirable.

I've either got to pull them off and have them fitted and rewelded, take a gamble on another pair (probably cheaper than the customizing of the first set), or maybe switch to a cheap pair of used OEM 97-99 manifolds which will have perfect fitment but will require another set of test pipes (or bungs to be welded in?)