I pretty much made a KA24DE engine but I don’t have a 98 240sx to put it in will there ever be a bodystyle and light like it to make one?
Eventually there will be a body type to match it yes. The lights however, maybe later. It is possible that you might have to wait until the devs finish the game and someone makes them as a modding addition to the game.
Just have to be content making FC Rx7 and S15 200sx clones until then =D
also be creative with parts you do have, like vents. Make them really thin on the hood of the car, to recreate a bit like pop-up headlights
Example: (quickly made this in under 2 minutes)
You can also use grilles it you need some more chrome on the car, though you can’t turn them and they don’t fit on the sides. But I think there is a chrome vent, too 
For the sides, use doorhandles which can be stretched really long. As for frontbumper and rear, you can use stretched vents indeed, or for 1 big long thing, you can use the badges by stretching them, too.