Hello ACW270,
The Series 1 cars are only different by small details:
S1 "bonded in" chassis, push button door handle, fixed windows, fixed seats, aluminium dash, Lancia rear lights
S1A: "bonded in" chassis, push button door handle, lift-out windows, fixed seats, wooden dash, Lancia rear lights
S1B: "bonded in" chassis, push button door handle, lift out windows, fixed seats, wooden dash, larger rectangular rear lights
S2: separate bolted chassis, early cars had S1B features but a different dashboard, electric windows (with a quarter light)
adjustable seats, followed by several changes to door handles, new front nacelle indicators and further body changes...