I finally complete the 99NB1 bumper cover changes to a 01'.
So for those planning to do something similar...here are some observations. And a big thanks to dliverance for his advises.
These bumper are a direct exchange fit....But you will need.
1. two special clips as dliverance noted
2. be prepared to have some new panel clips. Some of mine were missing or broken. (clips for the mudguard to bumper, clips for the mouth, 4 large rivets for the bumper to large mounting bracket to the frame.
3. The inner fender mudguards does not fit prefectly. In fact 2 of the holes for the mudguards does not line up to the bumper. If you want it to fit perfectly, you'll need 2 new 01' mudguard covers (one per side).
4. you'll need to source 2 foglights & their mounting bracktes
Now I gotta figure out how to power the foglights. My 99' has a live foglight button/switch on the dash. It lights up when pushed. Is this switch powered by a ciruit in the engine bay fuse box? If so, is it somehow "connected" or is it separate from the headlight fuse?.
Also for those planning to refit a Mazdaspeed front bumper cover to a 99-00, this also apply. But I'm not sure if the mudguards can be rigged to fit.