A Screwcutting Gearbox to fit both the ML7 and Super 7 lathes was introduced in late 1954. The box generated 48 threads from 8 to 56 t.p.i. and the same number of feeds (by the simple expedition of pulling out a double gear mounted on the banjo) of 0.139" to 0.002" per revolution of the spindle.
The gearbox is shown fitted to a very early Super 7, some distinguishing features of which were the use of large, knurled-edge threaded fasteners on the selector levers for tumble reverse, backgear and the gearbox and countershaft covers and  the integral headstock drip-feed oiler - the circular window of which can be seen just to the left of the chuck. This latter (expensive-to-make) feature was abandoned after 1959. Another picture of the early headstock can be seen HERE.

Screwcutting gearbox with the end cover open - fitted in this case to an ML7. The middle gear of the lower three reverses on its stud to select fine feeds or screwcutting.

Myford ML7R:
Introduced at more or less at the same time as the power cross feed Super 7, this is the lathe that confuses people new to the make. Although called an ML7 - and you would therefore expect it to be a development of, or directly related to, the original machine of that name - it was actually a non-power cross feed Super 7, but without a clutch and fitted with ML7 cross and top slides. It was designed to fit below the Super 7 in place of the ML7 and allowed a rationalisation of production around just one design of bed, headstock and tailstock. The lathe was eventually fitted with Super 7 cross and top slides, the ML7R name dropped and the "new" model renamed "Super 7 Sigma".