Guys, I know this is an old thread.
But I am reviving it because it is one of the few discussions of this engine-disconnect/neutral-return feature on the 140s. In doing some general parts research, I came across information which answers the o.p.'s question and maybe resolves this small mystery.
Jeff/jphavener was asking whether the later 140s have the engine disconnect feature. The answer is that it depends on how you define "later 140".
My 1972 140 H3 is usually considered a "later model". It has the 14 HP engine, dual drum steering brakes, the new style rear hydrostatic transmission, 1" front spindles, cassette style front wheel bearings, beefier rear axle, new style rear axles and hubs with inboard seals, etc.
And by depressing the left pedal, it also has both the neutral-return and the engine-disconnect feature, just like Glockem's (I believe he was referring to his 1971).
However, the engine disconnect feature was eliminated on 140 H3 models in early 1973 starting with Ser. # 46884. For H1 models, the engine disconnect feature was elminated at the beginning of model year 1972 starting with Ser. # 38001. Note that the change occured at the beginning of 1972 for H1, and a very short-way into model year 1973 for H3 models.
In the schematics below, the first has a clutch assembly (part# 13) which the second lacks. The entire first assembly is called the "engine disconnect drive shaft" style, and the second is simply called the "driveshaft" assembly.
So among the later model 140s, all H1s from 1972 and later will lack the engine disconnect feature. With H3 models, nearly all '73 and all '74 models will lack the engine disconnect feature. 1972 H3s and a very few early '73s have the engine disconnect feature.