I don't recall the national 300, but had an ncx-300, my first radio.  I 
wish I'd kept it.  all tubes except the vfo, but I digress, that was a 
transceiver.  I do have a kenwood R-300, all solid state and out in late 
seventies as I recall.  I finally found on on e-bay as I had sold mine 
years ago.  Very rare, but a neat receiver.
73s
Butch Bussen
wa0vjr