Electric Fan Cfm Sizing ?

I would upgrade to a 3 row aluminum radiator at least and go with the most cfm you can get. You never know when you'll end up in stop and go traffic on the hottest day of the year. But realistically your radiator with a 2500 cfm should be sufficient. Especially if you put a shroud on with it.
I am running a 3 row Champion radiator with a fan I believe is a 16 inch but not quite 2500 cfm on a 347 stroker and haven't had an issue with overheating, but then I'm in ohio and haven't run my AC in stop and go traffic yet either.
Be safe and go big then you don't have to worry.

I ended up aiming for a 3000cfm rating and going with dual S blade 12" fans on a factory 3 row rad for my 4v clevland it has no cooling issues going through slow traffic on a hot day, no shrouding on them either they are just direct mounted to the rad. If I get cooling issues I'll shroud them. I would think that 2500cfm would probably do the job if the cooling system is in decent shape.