I want to put after market flexlite radiator and fans in my 1989 iroc. 350 can I bypass factory wiring ? And use after market?

Absolutely, the fan relays are engine controlled but have no feed back and won't set trouble codes. Just make sure they work enough to properly keep engine cool.

Yes you can but you should use a relay to power the fans on and off. This will make it easier and a cleaner install plus reducing the size of wire needed for the control circuit. You should also install a thermostat to turn the fans on and off and do your research on the size of the fans. You dont want to do all this and they not move enough air.

You could, but if you do that, no matter what, always add a fused circuit. All the circuit would have to be is a thermostat, a connection to the battery, the fan, and a fuse, but always have the fuse.