This is the gauge cluster from a December of 78 build car.
79 RX7 gauges by
Kevin Frank, on Flickr
The 1979 model cars also had perforations in the dash pad for a speaker on the right side of the dash.
I believe that you have a very early build 1980 model. It would have been one of the first off the line with that build date. Arguably even cooler than a late build 1979 model if I'm correct.
Most people advise not to use synthetic oil. I would stick to the factory recommended oil in a non-synthetic if I were you.