All M14 rifles made by the real Springfield Armory, H&R, Winchester and TRW were selective fire. Most issue rifles had a removeable selector lock in place of the selector switch, making them temporarily a semiautomatic only rifle.
Some selective fire M14s may have been made by Smith Enterprise and Springfield Armory, Inc. I'm not really certain.
The main difference between the M14 and M1A is the selector stud, connecting rod and selector parts on the M14. The op rod on the M14 is also supported by the connector rod and has a mid-receiver dissassembly notch. The M1A lacks the selector stud and supports the op rod with, for the lack of a better term, a shelf under the op rod. The op rod dissassembly notch is at the rear.
M-K Specialties is reportedly selling new, forged receiver M14 semi auto rifles. I haven't seen one, but if you have one of their "remanufactured" M14 receivers and you haven't received a call from the BATF about it, you may hear from them soon.
The M1A pictured above appears to have one of Fred's kinda cheesy looking selector cutout fillers that resembles the selector lock and the end of the connector rod.