I don't know how your radiator lines up to anything to reference on your car (obviously) or how the radiator is built, but this is what I did...
I got a Fluidyne radiator and after setting it in realized there wasn't a chance in hell that I'd be able to secure the top with the stock mounts. They were miles away from lining up. So I drilled two holes in the top metal frame part of the radiator (NOT the finned area of the radiator itself!) and two in the body of the car and just secured it with two bolts.