The 7998 is a tight deck. Being the superficial bastard that I am, I really like the fact that its faceplace covers the entire din and a half opening on the gm truck.
I dont have this deck, but it is definitely #1 on my list right now. The biolite display looks sick. I think you are gonna get some kick ass SQ from that deck.
I would go for a JL Stealthbox under the back seat. It has a 12" sub..screw the 8!
Definitely go with some 6.5" components in the front doors. Maybe the Alpine SPS-171A. Alpine 4x6 for the back.. SPS-460A.
Let me know how it sounds

cause thats the setup I want.