I completed a swap in mine, 6.0 into a 1992. I am not sure if the thottle cable from the 99 will work but I used a throttle cable from a 96-98 vortec pickup and worked perfect

you will need an adapter. (metric to standard) to use the oil pressure sending unit from the old tbi in the new motor if you are going to use factory gauges
you will also need an adapter for the temp sending unit
high pressure fuel pump for vortec and fuel line adapters.
I left the ls temp sending unit in place for pcm and moved the tbi temp sending unit to the plug in the passenger side head for factory gauge
lt1swap is a great resource for wiring. what type of relays to use etc. I also picked up a haynes manual for the ls wiring diagrams.
pcm will need to programmed to remove anti theft also