Im shure you didn't have the 2.8 because the last year it was it the camaro was 89...lucky me
I think the V6 would have been a 3.1, but I dont know for shure...
Was the fan switched when the engine was switched? I know the V8s needed more air pulled through the radiator...I think they have a dual fan setup.
If the fan wasnt switched at the time of swap, I would recommend going to a salvage yard and getting the dual fan setup out of a v8 camaro...you might also need a bigger radiator...
Dont drive your car around until you get this fixed, you dont want to overheat that new engine...would be a shame...