First, between the two choices of new radiator, I'd select the Nissens, but try to find out if it comes with the brass sleeve insert. And, no, the repacement radators are all still an aluminum core with plastic tanks, but SOME will have a brass insert in the upper tank hose connection inlet. I can't find any all metal replacements anywhere...
Second, as for repair, you could insert a brass or even another metal sleeve into the interior of the neck, and fix with epoxy, but be sure the expoxy is both temperature and water resistant. Check the archives, there's a specific brand listed in a previous thread. Also you can get some resources from
www.imcool.com.
Finally, here's a pic for a very temporary fix: