Two engine builders have told me many new cars and new engines use the aluminium powder to take care of situations like your radiator. Every engine I have built or had built has had the bars stop leak put into the radiator just after the dyno. The radiator stop leak also serves as a lubricant for your water pump too. If you are going to track your car you cannot run
antifreeze which among other things has a lubricating property. Buy a pint of the Aluminium Bars Stop leak and follow the instructions. I think you will be pleased. The StopLeak will also help with electrolisys of dis-similar metals (aluminium and steel) which is a whole different problem.
Clois Harlan