I can add some information regarding the Plus 4s from 1950-68:
1. Narrow Body, High Profile, 1950-1957. The Plus 4 was 2 inches wider than the 1936-50 4/4 Series 1. The change from Flat rad to Waterfall grille did not change the body sizes.
2. Wide Body, High Profile, 1957-1968. The cockpit was widened by 2 inches and the fenders were narrowed accordingly. The transition was made first for 2-seat roadsters, and four-seaters were widened in 1958.
3. Narrow-body, Low-Profile, 1961-1968. All but the first few SuperSports were fitted with the smaller 4/4 bodies. In 1967-68 the 4/4 body became standard on Plus 4 roadsters but not 4-seaters. But some of the 1967 +4 roadsters were built with the wide-body as per previous years.
4. Wide body, Low Profile. 1967-68. Some of the last +4 roadsters appear to have wider bodies as on later 4/4s.
The trends in 4/4s from 1954 to 1968 were a little different and hopefully someone else can help.
