1974 Stadium open face (there weren't many full-face lids around then but you could by a visor with a coloured lower section so that it looked like a full-face!).
Bought my first Shoei full-face in 1975. It cost me £40 back then and I only took home about £60 a month!
I stuck with Shoei for years and also had BMW System from II onwards.
I love Shoei, they always seem to touch in all the right places and would have stuck with them but until relatively recently, they didn't produce a flip-front. My last Shoei, an X8R is still in first class condition but I just don't wear it any more.
System II, good peripheral vision. The flat curve of the visor really helped shed water. The heated visor was a nice but very pricey bit of kit and the elements didn't last too long.
System III, better shape but a lot heavier.
System IV. Still the best System helmet IMO. The weight, peripheral vision and ventilation all work well. The best thing about it is the fact that it's really three helmets if you buy the cheek pieces and the peak.
The removal of the visor and the chin bar takes seconds, it can be worn as an open face, full face, with chin bar + peak with goggles. On a trip I carry the cheek pieces and the peak plus goggles and swap the configuration according to the use or conditions.
System V. Nice vents, except the chin bar one that is too fiddly and closes every time you touch it. Not noticeably lighter than the IV and certainly not any quieter, take the chin bar gusset out and it's very noisy. I don't like the V-shaped visor. Easier to fit ear-pieces in as it was designed with them in mind (for once). NO peak available so less options for change.
System V is a disappointment after the IV IMO. It took me much longer to get used to it than the IV and I only persisted so that I can extend the life of my IV.
but have to say it's great for comfort/vision and looks 
