Compatible Parts
 

So I bought a 99 a4 at the beginning of this year I ended up buying a new engine for it and rebuilding it with my old man, we're done with the engine and everything under the hood but now I'm looking for exterior parts such as hood and bumper, and I'm curious to know if a 2001 a4 or a 98 a4 quattro bumper and hood would fit my 99 a4

There was a facelift of the A4 in mid 1999 (commonly called the 99.5 update).
So it depends whether your car is a pre or post facelift as to which bumper (from the 98 or 01) is most suitable.
The visual difference is pre facelift bumpers have a three piece lower grill.
The post facelift bumper has one continuous lower grill with built-in foglights at each corner.

If you don't know what your original bumper looked like, another indication is the headlights, pre facelift have separated headlights and indicators and the headlights have a glass lense.
Post facelift have a 1 piece headlight and indicator assembly with a clear PVC lense.

The other indication is obviously the build date, but I'm not sure of the change over date.

If all you're concerned about is fitment, both bumpers should fit.

Both bonnets (hoods) will be the same - there weren't any major sheetmetal changes between pre/post facelift.

Alright thanks, mine is a post face lift it has clear pvc lenses.With that said which bumper would be most suitable for my 99 post face lift a4?

The one off the 01 would be the same design as the one originally on your car.