Harold: MT coupler springs are in the shank, in the draft gear box. You're right, they don't get lost in service.
The McHenry springs are on the coupler itself, to hold the knuckle closed, like the KD HO couplers. They do get lost, and then the couplers don't work.
As for a rigidly mounted coupler on the pilot beam, it will work, and was done years ago when the only N scale knuckle coupler was the 1025. Usually only the knuckle portion was used, so that the mating coupler could still be uncoupled. As long as the McHenry can be line up with the other coupler, it will couple, and uncouple, even if rigidly mounted.
And I often have to manually align N scale couplers on curves, usually because cars have different coupler overhangs. The same pick used for uncoupling can be used to nudge the couplers into alignment.