I am not so sure that a 914/4 could be ordered with a USA market radio from the factory, I have not seen any evidence of that, but I do not have any factory USA-market price lists.
The antenna may have been orderable because the car is set up for that on the inside fender wall, but I have not taken an original paint car apart to see if the antenna hole was factory. I need to do that.
I have price lists from Germany for German market 914s that indicated the availability of German market radios mostly for /6s, but also for 914/4 German market 914s. The only price list I have from a USA dealership suggests the radios offered were only dealer installed, USA market radios - Blaupunkt, Motorola, etc.
http://bowlsby.net/914/Classic/OpEq.htmA list of some of the USA radios available, and note that USA market "Radio Installation Kits" from Blaupunkt and Motorola were available:
http://bowlsby.net/914/Classic/Accessories.htm