Because the camaro's came TBI as well, and it's the same vintage. Truck setup uses all the same stuff the car does (AFAIK) so the re-pin should be exactly the same.
For the stock harness scaring everyone, I'd sure like to know why. I think I pulled the alternator and AC wires out of my stock TPI harness, and besides the AIR and EVAP (which are tied up out of the way) all are plugged in/reused. All connections are keyed and only go to one component, so an aftermarket harness can't be any simpler, (minus the AC or alternator which is about 4 wires and two connectors) unless it's missing components.
If you don't have the appropriate wiring manual for the harness, it might be scary, but anyone that knows TPI can work on my truck and troubleshoot it with a factory manual. (even though I'm the only one doing it)
And if you don't think the factory manual is an advantage, wait until something doesn't work and you have to figure out which component it is. BTDT, factory manual paid for itself the first time.