What modifications would i need to make to drop a 2000 ld9 engine into my 1998 z24 plz..

i just did this last week..
you need to:

Switch exhaust manifold from old to new engine
Keep your fuel raul and injectors from old engine
Take off new kncok sensor. drill out new hole for old knock sensor (youll know wut i mean when you look at it)
youll also have an EGR check engine light since the new engine doesnt have EGR
Change old upper engine mount to new engine.

im pretty sure thats it its all bolt on stuff easy to do except drill out hole for knock sensor which is pretty easy too. you can hit me up if u need any help

can a dealership delete the code for the egr check lite?

no you can try an egr simulator.. some work some dont.

You could run a 99 harness and PCM... then you can use the 2000 injectors, and everything (no EGR on 99's). The 99-02 engine is the same, except the first O2 sensor is one wire on 99 and two wires 00-02.