I'm not a fan of those little sirocco style rads. I had one a long time ago, with a small block in the car and it was un-raceable. By the time I drove to the staging lane, pulled up with 50-60 other cars, did a burn out, staged the car, made a run, drove to the ticket shack, then drove to the pits. It would severely overheat.. Back then I fixed that with a stock rad out of a 70's dodge truck. I now have a multiple tube core aluminum rad. I think those rads you have is something like a single tube core at 13" by 20". not enough rad is my Restrictors in the manifold probably don't help either. Could you drill them from the fitting end?