I think what is different is the mounting holes on that after market radiator. I have encountered that in the past. What I wound up using was larger sell taping screws, kind of like a license plate screw only for metal. Like the screws holding your voltage regulator on or the ground wires on the radiator core support. I screwed them right in the radiator hole without a speed clip. Hope this helps.
Thanks. Unfortunately I was afraid of this. The mounting tabs look correct but as you say it is the holes that appear to be the problem. This soulution doesn't sound too bad though. I will know more when I line the shroud up tomorrow. Thanks SG!