I just did this. With some modifications the fan fits very nicely into the stock fan shroud. Looks like it's supposed to be there and is secured with the factory bolts. It can be very easily installed and removed. I started with a '96 and up shroud, not sure if they are different on the non Vortec trucks.
1- Trim all the tabs off the Camaro fans.
2- The bottom of the Camaro fans has a bowed out portion that prevents it from fitting all the way down in the core support, place a straight edge across and cut that off. ( not sure if this is really necesary, as I was trying a different mounting scheme at this point)
3- On the shroud there is a moled in line that goes all the way around. It starts just behind where the channel is for the wire that runs across the top and goes between the battery and fuse block. Cut the shroud along that line all the way around.
4- The Camaro fans now fit snugly in the shroud along the top and bottom. I used screws to attach here. There will be a one inch gap on the left and right side, I used great stuff foam to seal it up and painted it black.
Mike