I purchased a new radiator on amazon for my 7/71 240Z that actually looks quite nice.  The problem is there are two ports at the bottom of the radiator.  The ports are 14MM threads.  I went to every hardware, auto, and home improvement store to find a cap that would screw on to cap the holes, but they're not made in metric.  I believe the ports are for a 280Z.

Any suggestions as to how to cap them?

Ignore them. They are for the coolant lines for an automatic transmission. If you are worried about fluid getting into them for corrosion purposes, fill them with RTV.

To be clear, the channel between the two ports does not affect the rest of the radiator, correct?  I'm kicking myself for not checking that.  If that's the case, I will put some RTV in the holes.  Thank you for your insight.

Steve J is of course correct.  The do not affect the main cooling area of the radiator.   Many of the aftemarket manufacturers standardized on one model which includes the section for the auto transmission. 

Thanks to all...you've been most helpful.