Ok (not gonna quote the big post there), so I'm not sure about the 'core support' there but I'll try to answer what you've said.
1. I did NOT need any sort of support mechanisms for my 01 to 96 conversion. I assume since those are even more different than the 98-00 trucks, than you don't either.
2. Therefore, I think I have to agree with what 'scuba' posted. It is mostly bolt-on. Any additional modification is outlined in my grille swap thread.
3. If you remove your grille and lights and take a picture and post it on here, I can better help you and compare it to the pictures I have of each of my trucks' front ends disassembled. We can compare sub frame structures.
4. Despite whatever else you read/find, I am sticking to my guns that you DO NOT need new corner lights or fenders. I didn't in my conversion, so you don't either.
5. You will need the entire headlight assembly. This includes the 'shell' that the headlight goes in, the aiming hardware (plastic plugs and screws basically), and the metal headlight surround that holds then entire lens into the assembly. I couldn't find it on rockauto
, but then again I suck at searching on there so who knows.
6. You don't need to buy sealed beams. I have the IPF rectangular lenses and H4 bulbs. You can run that.
Hope it helps. I am only replying from my experience though too.