My Radiator Cracked

This weekend my radiator cracked at the filler neck. It may be able to be fixed but I think it is the rad from the slant six that the PO replaced with a 318. I am building a 340 for it now so what would be the best rad for a 340 auto w/o ac. I know the aluminum ones are more $$ is it worth it? Want to get a good one that will last and run cool.

Any opinions insight on which one to get would be helpful.

Thanks!

Justin