Hi Simon
From what I have researched, the 1978 series 1 spyder should have the "thin reflector". he larger lenses were predominately use for USA cars and some later series 2 cars. if your interested to make them the same, I can help you as I have remanufactured them. Just PM me .
Hi Angelo, Simon
The Series 1 never came as 2 litre, so definitely a S2 and 78 would indicate probably a facelift, a black interior would most likely confirm it. I would suspect that the larger reflector is most likely the original type if it is, but not sure when they changed. I know there are a few S2 pre f/l cars with the larger reflector and think it was only the early ones which had the carry over from the S1 with the smaller reflector.
Simon, if you wanted to swap the small reflector for a large one, I would be interested as have a few of the large ones in my spares stock. If you want to go small reflector, then Angelo is your man.
Peter