Ford stopped producing the parts so they weren't able to make the kits anymore. An eaton swap would be a better choice anyway. With the KB kit you were stuck with the 2.1.
However, if I was starting with a car with no blower I'd go centri personally.
Ford was not associated with the KB sc for the 99-01 Cobras.
KB made a one time batch for the Cobras and was done.
We had to sign up and put up a deposit for the kits.
KB returned the deposits and let those who signed up, buy or not at their choice.
The kits came with a 1.9L supercharger, I think. I do have one on my 99 Cobra. Recommended max boost was 9 lbs.
The kits were well designed and produced 445 to 465
whp.
I think Jim Christain was KB head engineer and was available for the kit owners question answer line.
The 2 valve and 3 valve kits might be available, but doubt them having a kit for the 4V 4.6.
Hope this helps in your decision.
Early kits were 1.9. Later on the kits has 2.1's. That's what they came with when I was looking for my 01. Some of the pieces for the kits were sourced from Ford. Not the whole kit.